feat(handoff): introduce firmware handoff library

Add transfer list APIs and firmware handoff build option.

Change-Id: I68a0ace22c7e50fcdacd101eb76b271d7b76d8ff
Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
diff --git a/Makefile b/Makefile
index 1cce234..104d84d 100644
--- a/Makefile
+++ b/Makefile
@@ -1027,6 +1027,10 @@
         $(info DRTM_SUPPORT is an experimental feature)
 endif
 
+ifeq (${TRANSFER_LIST},1)
+        $(info TRANSFER_LIST is an experimental feature)
+endif
+
 ifeq (${ENABLE_RME},1)
 	ifneq (${SEPARATE_CODE_AND_RODATA},1)
                 $(error `ENABLE_RME=1` requires `SEPARATE_CODE_AND_RODATA=1`)
@@ -1191,6 +1195,7 @@
 	SPMC_AT_EL3 \
 	SPMD_SPM_AT_SEL2 \
 	ENABLE_SPMD_LP \
+	TRANSFER_LIST \
 	TRUSTED_BOARD_BOOT \
 	USE_COHERENT_MEM \
 	USE_DEBUGFS \
@@ -1351,6 +1356,7 @@
 	SPM_MM \
 	SPMC_AT_EL3 \
 	SPMD_SPM_AT_SEL2 \
+	TRANSFER_LIST \
 	TRUSTED_BOARD_BOOT \
 	CRYPTO_SUPPORT \
 	TRNG_SUPPORT \