feat(spmc): enable the SPMC to pass the linear core ID in a register

Add TF-A implementation defined behaviour to provide the linear core
ID in the x4 register when bringing up an SP.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: I6cb215841097b264d252ec0262b0b7272be99d41
diff --git a/services/std_svc/spm/el3_spmc/spmc_setup.c b/services/std_svc/spm/el3_spmc/spmc_setup.c
index 7b23c9e..af5219d 100644
--- a/services/std_svc/spm/el3_spmc/spmc_setup.c
+++ b/services/std_svc/spm/el3_spmc/spmc_setup.c
@@ -44,6 +44,12 @@
 				DISABLE_ALL_EXCEPTIONS);
 
 	/*
+	 * TF-A Implementation defined behaviour to provide the linear
+	 * core ID in the x4 register.
+	 */
+	ep_info->args.arg4 = (uintptr_t) plat_my_core_pos();
+
+	/*
 	 * Check whether setup is being performed for the primary or a secondary
 	 * execution context. In the latter case, indicate to the SP that this
 	 * is a warm boot.