feat(lib/psa): mock PSA APIs

Introduce PLAT_RSS_NOT_SUPPORTED build config to
provide a mocked version of PSA APIs. The goal is
to test the RSS backend based measured boot and
attestation token request integration on such
a platform (AEM FVP) where RSS is otherwise
unsupported. The mocked PSA API version does
not send a request to the RSS, it only returns
with success and hard-coded values.

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Change-Id: Ice8d174adf828c1df08fc589f0e17abd1e382a4d
diff --git a/Makefile b/Makefile
index 16c85bc..b42bdc5 100644
--- a/Makefile
+++ b/Makefile
@@ -1011,6 +1011,7 @@
         NS_TIMER_SWITCH \
         OVERRIDE_LIBC \
         PL011_GENERIC_UART \
+        PLAT_RSS_NOT_SUPPORTED \
         PROGRAMMABLE_RESET_ADDRESS \
         PSCI_EXTENDED_STATE_ID \
         RESET_TO_BL31 \
@@ -1146,6 +1147,7 @@
         NS_TIMER_SWITCH \
         PL011_GENERIC_UART \
         PLAT_${PLAT} \
+        PLAT_RSS_NOT_SUPPORTED \
         PROGRAMMABLE_RESET_ADDRESS \
         PSCI_EXTENDED_STATE_ID \
         RAS_EXTENSION \