feat(intel): enable SDMMC frontdoor load for ATF->Linux

SDMMC is 1 of the boot source for Agilex5 and legacy products.
By enabling this, ATF is able to read out the DTB binary and
loaded it to DDR for Linux boot.

Change-Id: Ida303fb43ea63013a08083ce65952c5ad4e28f93
Signed-off-by: Jit Loon Lim <jit.loon.lim@intel.com>
Signed-off-by: Sieu Mun Tang <sieu.mun.tang@intel.com>
diff --git a/plat/intel/soc/agilex5/platform.mk b/plat/intel/soc/agilex5/platform.mk
index 546bc2e..f4d3b7d 100644
--- a/plat/intel/soc/agilex5/platform.mk
+++ b/plat/intel/soc/agilex5/platform.mk
@@ -99,6 +99,10 @@
 CTX_INCLUDE_AARCH32_REGS := 0
 ERRATA_A55_1530923 := 1
 
+# Don't have the Linux kernel as a BL33 image by default
+ARM_LINUX_KERNEL_AS_BL33	:=	0
+$(eval $(call assert_boolean,ARM_LINUX_KERNEL_AS_BL33))
+$(eval $(call add_define,ARM_LINUX_KERNEL_AS_BL33))
 $(eval $(call add_define,ARM_PRELOADED_DTB_BASE))
 
 PROGRAMMABLE_RESET_ADDRESS	:= 0