PlatformSP: Add Platform service

TF-M Platform service is a trusted service which allows secure
partitions and non-secure applications to interact with some
platform-specific components. There are a number of features which
requires some interaction with platform-specific components which
are at the same time essential for the security of the system.
Therefore, those components need to be handled by a secure partition
which is part of the trusted compute base.

This patch adds the Platform service which provides the system reset
as a first function.

Change-Id: I68253328db22a45fb6a3d6820dd85b1e24ea96f0
Signed-off-by: Marc Moreno <marc.morenoberengue@arm.com>
diff --git a/platform/include/tfm_plat_crypto_keys.h b/platform/include/tfm_plat_crypto_keys.h
index dc2b076..9682cc9 100644
--- a/platform/include/tfm_plat_crypto_keys.h
+++ b/platform/include/tfm_plat_crypto_keys.h
@@ -25,7 +25,7 @@
  * \param[out] key   Buf to store the key in
  * \param[in]  size  Size of the buffer
  *
- * \return Returns error code specified in \ref tfm_plat_errno_t
+ * \return Returns error code specified in \ref tfm_plat_err_t
  */
 enum tfm_plat_err_t tfm_plat_get_crypto_huk(uint8_t *key, uint32_t size);