arm: omap5: add U-Boot FIT signing and SPL image post-processing

Modify the SPL build procedure for AM57xx and DRA7xx high-security (HS)
device variants to create a secure u-boot_HS.img FIT blob that contains
U-Boot and DTB artifacts signed with a TI-specific process based on the
CONFIG_TI_SECURE_DEVICE config option and the externally-provided image
signing tool.

Also populate the corresponding FIT image post processing call to be
performed during SPL runtime.

Signed-off-by: Daniel Allred <d-allred@ti.com>
Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/cpu/armv7/omap5/config.mk b/arch/arm/cpu/armv7/omap5/config.mk
index a7e55a5..d245572 100644
--- a/arch/arm/cpu/armv7/omap5/config.mk
+++ b/arch/arm/cpu/armv7/omap5/config.mk
@@ -15,5 +15,8 @@
 ALL-y	+= MLO
 endif
 else
+ifeq ($(CONFIG_TI_SECURE_DEVICE),y)
+ALL-y   += u-boot_HS.img
+endif
 ALL-y	+= u-boot.img
 endif