SMCCC/PCI: Handle std svc boilerplate

Add SMC wrappers for handshaking the existence
and basic parameter validation for the SMCCC/PCI
API. The actual read/write/segment validation is
implemented by a given platform which will enable
the API by defining SMC_PCI_SUPPORT.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Change-Id: I4485ad0fe6003cec6f5eedef688914d100513c21
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index 2088533..1fdf545 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -95,6 +95,10 @@
 				lib/cpus/aarch64/wa_cve_2017_5715_mmu.S
 endif
 
+ifeq ($(SMC_PCI_SUPPORT),1)
+BL31_SOURCES		+=	services/std_svc/pci_svc.c
+endif
+
 BL31_LINKERFILE		:=	bl31/bl31.ld.S
 
 # Flag used to indicate if Crash reporting via console should be included