feat(arm): add trusty_sp_fw_config build option

Also increase add PLAT_ARM_SP_MAX_SIZE to override the default
ARM_SP_MAX_SIZE to support Trusty image and move OPTEE_SP_FW_CONFIG
documentation to build-internals.rst as it's not externally set-able.

Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ief90ae9113d32265ee2200f35f3e517b7b9a4bea
diff --git a/Makefile b/Makefile
index 2892f21..6a1ea99 100644
--- a/Makefile
+++ b/Makefile
@@ -452,8 +452,12 @@
 			DTC_CPPFLAGS	+=	-DOPTEE_SP_FW_CONFIG
 		endif
 
+		ifeq ($(findstring trusty_sp,$(ARM_SPMC_MANIFEST_DTS)),trusty_sp)
+			DTC_CPPFLAGS	+=	-DTRUSTY_SP_FW_CONFIG
+		endif
+
 		ifeq ($(TS_SP_FW_CONFIG),1)
-		DTC_CPPFLAGS	+=	-DTS_SP_FW_CONFIG
+			DTC_CPPFLAGS	+=	-DTS_SP_FW_CONFIG
 		endif
 
 		ifneq ($(ARM_BL2_SP_LIST_DTS),)