docs(arm): update docs to reflect rotpk key changes

The hashing algorithm for the rotpk is now HASH_ALG,
not always sha-256. The public development keys are
no longer in the repository and are now generated at
run-time, updates the documentation to reflect this.

Change-Id: Ic336f7aca858e9b6a1af6d6e6dc5f4aa428da179
Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/docs/plat/arm/arm-build-options.rst b/docs/plat/arm/arm-build-options.rst
index afbb157..a086a98 100644
--- a/docs/plat/arm/arm-build-options.rst
+++ b/docs/plat/arm/arm-build-options.rst
@@ -65,25 +65,26 @@
    -  ``regs`` : return the ROTPK hash stored in the Trusted root-key storage
       registers.
    -  ``devel_rsa`` : return a development public key hash embedded in the BL1
-      and BL2 binaries. This hash has been obtained from the RSA public key
-      ``arm_rotpk_rsa.der``, located in ``plat/arm/board/common/rotpk``. To use
-      this option, ``arm_rotprivk_rsa.pem`` must be specified as ``ROT_KEY``
-      when creating the certificates.
+      and BL2 binaries. This hash corresponds to the development private key
+      ``plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem``.
+      The hashing algorithm is selected by ``HASH_ALG``; sha256 is used if
+      ``HASH_ALG`` is not specified. A different RSA key can be specified by setting
+      ``ROT_KEY``, there are 3k and 4k RSA keys in ``plat/arm/board/common/rotpk/``.
    -  ``devel_ecdsa`` : return a development public key hash embedded in the BL1
-      and BL2 binaries. This hash has been obtained from the ECDSA public key
-      ``arm_rotpk_ecdsa.der``, located in ``plat/arm/board/common/rotpk``. To
-      use this option, ``arm_rotprivk_ecdsa.pem`` must be specified as
-      ``ROT_KEY`` when creating the certificates.
-   -  ``devel_full_dev_rsa_key`` : returns a development public key embedded in
-      the BL1 and BL2 binaries. This key has been obtained from the RSA public
-      key ``arm_rotpk_rsa.der``, located in ``plat/arm/board/common/rotpk``.
-
--  ``ARM_ROTPK_HASH``: used when ``ARM_ROTPK_LOCATION=devel_*``, excluding
-   ``devel_full_dev_rsa_key``. Specifies the location of the ROTPK hash. Not
-   expected to be a build option. This defaults to
-   ``plat/arm/board/common/rotpk/*_sha256.bin`` depending on the specified
-   algorithm. Providing ``ROT_KEY`` enforces generation of the hash from the
-   ``ROT_KEY`` and overwrites the default hash file.
+      and BL2 binaries. This hash corresponds to the development private key
+      ``plat/arm/board/common/rotpk/arm_rotprivk_ecdsa.pem`` unless a different key
+      is specified with ``ROT_KEY``, such as the 384 bit key in the same directory.
+      he hashing algorithm is selected by ``HASH_ALG``; sha256 is used if ``HASH_ALG``
+      is not specified.
+   -  ``devel_full_dev_rsa_key`` : return a development public key embedded in
+      the BL1 and BL2 binaries. This key corresponds to the RSA private
+      key ``plat/arm/board/common/rotpk/arm_rotprivk.pem`` by default, but can
+      be changed by setting ``ROT_KEY``, there are 3k and 4k RSA keys in
+      ``plat/arm/board/common/rotpk/``.
+   - ``devel_full_dev_ecdsa_key`` : return a development public key embedded in
+      the BL1 and BL2 binaries. This key corresponds to the EC private key
+      ``plat/arm/board/common/rotpk/arm_rotprivk_ecdsa.pem``, unless a different
+      ECDSA key is specified by ``ROT_KEY``, such as the 384 bit key in the same directory.
 
 -  ``ARM_TSP_RAM_LOCATION``: location of the TSP binary. Options: