doc: Misc syntax and spelling fixes

Tidying up a few Sphinx warnings that had built-up over time.
None of these are critical but it cleans up the Sphinx output.

At the same time, fixing some spelling errors that were detected.

Change-Id: I38209e235481eed287f8008c6de9dedd6b12ab2e
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/getting_started/porting-guide.rst b/docs/getting_started/porting-guide.rst
index d715769..9cca75e 100644
--- a/docs/getting_started/porting-guide.rst
+++ b/docs/getting_started/porting-guide.rst
@@ -549,7 +549,7 @@
 -  **PLAT_PARTITION_BLOCK_SIZE**
    The size of partition block. It could be either 512 bytes or 4096 bytes.
    The default value is 512.
-   `For example, define the build flag in platform.mk`_:
+   For example, define the build flag in ``platform.mk``:
    PLAT_PARTITION_BLOCK_SIZE := 4096
    $(eval $(call add_define,PLAT_PARTITION_BLOCK_SIZE))
 
@@ -954,7 +954,7 @@
     Return   : void
 
 A platform may need to do additional initialization after reset. This function
-allows the platform to do the platform specific intializations. Platform
+allows the platform to do the platform specific initializations. Platform
 specific errata workarounds could also be implemented here. The API should
 preserve the values of callee saved registers x19 to x29.
 
@@ -2777,7 +2777,7 @@
 added to the local implementation.
 
 Some C headers have been obtained from `FreeBSD`_ and `SCC`_, while others have
-been written specifically for TF-A. Fome implementation files have been obtained
+been written specifically for TF-A. Some implementation files have been obtained
 from `FreeBSD`_, others have been written specifically for TF-A as well. The
 files can be found in ``include/lib/libc`` and ``lib/libc``.