feat(drtm): add standard DRTM service

Added a dummy DRTM setup function and also, introduced DRTM SMCs
handling as per DRTM spec [1]. Few basic SMCs are handled in this
change such as ARM_DRTM_SVC_VERSION and ARM_DRTM_SVC_FEATURES
that returns DRTM version and functions ids supported respectively,
and others are dummy for now.

[1]: https://developer.arm.com/documentation/den0113/latest

Signed-off-by: Manish V Badarkhe <manish.badarkhe@arm.com>
Signed-off-by: Lucian Paul-Trifu <lucian.paultrifu@gmail.com>
Change-Id: I8c7afe920c78e064cbab2298f59e6837c70ba8ff
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index 3964469..878cea5 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -147,6 +147,10 @@
 BL31_SOURCES		+=	common/feat_detect.c
 endif
 
+ifeq (${DRTM_SUPPORT},1)
+BL31_SOURCES		+=	services/std_svc/drtm/drtm_main.c
+endif
+
 BL31_LINKERFILE		:=	bl31/bl31.ld.S
 
 # Flag used to indicate if Crash reporting via console should be included