feat(plat/versal): add support for SLS mitigation

This patch adds the option HARDEN_SLS_ALL that can be used to enable
the -mharden-sls=all, which mitigates the straight-line speculation
vulnerability. Enable this by adding the option HARDEN_SLS_ALL=1,
default this will be disabled.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@xilinx.com>
Change-Id: I0d498d9e96903fcb879993ad491949f6f17769b2

docs/plat/xilinx-versal.rst

@@ -24,6 +24,11 @@ To build TF-A for JTAG DCC console
 make RESET_TO_BL31=1 CROSS_COMPILE=aarch64-none-elf- PLAT=versal bl31 VERSAL_CONSOLE=dcc
 ```
 
+To build TF-A with Straight-Line Speculation(SLS)
+```bash
+make RESET_TO_BL31=1 CROSS_COMPILE=aarch64-none-elf- PLAT=versal bl31 HARDEN_SLS_ALL=1
+```
+
 Xilinx Versal platform specific build options
 ---------------------------------------------
 

plat/xilinx/versal/platform.mk

@@ -9,6 +9,7 @@ SEPARATE_CODE_AND_RODATA := 1
 override RESET_TO_BL31 := 1
 PL011_GENERIC_UART := 1
 IPI_CRC_CHECK := 0
+HARDEN_SLS_ALL := 0
 
 ifdef VERSAL_ATF_MEM_BASE
     $(eval $(call add_define,VERSAL_ATF_MEM_BASE))
@@ -87,3 +88,7 @@ BL31_SOURCES		+=	drivers/arm/cci/cci.c				\
 				plat/xilinx/versal/pm_service/pm_svc_main.c	\
 				plat/xilinx/versal/pm_service/pm_api_sys.c	\
 				plat/xilinx/versal/pm_service/pm_client.c
+
+ifeq ($(HARDEN_SLS_ALL), 1)
+TF_CFLAGS_aarch64      +=      -mharden-sls=all
+endif