ARM: Keystone2: Build secure images for K2

Adds an additional image type needed for supporting secure keystone
devices. The build generates u-boot_HS_MLO which can be used to boot
from all media on secure keystone devices.
Signed-off-by: NMadan Srinivas <madans@ti.com>
Signed-off-by: NAndrew F. Davis <afd@ti.com>
Reviewed-by: NTom Rini <trini@konsulko.com>
Reviewed-by: NLokesh Vutla <lokeshvutla@ti.com>

arch/arm/mach-keystone/config.mk

@@ -5,9 +5,15 @@
 # SPDX-License-Identifier:     GPL-2.0+
 #
 
+include  $(srctree)/arch/arm/mach-omap2/config_secure.mk
+
 ifndef CONFIG_SPL_BUILD
+ifeq ($(CONFIG_TI_SECURE_DEVICE),y)
+ALL-y += u-boot_HS_MLO
+else
 ALL-y += MLO
 endif
+endif
 
 MKIMAGEFLAGS_u-boot-spl.gph = -A $(ARCH) -T gpimage -C none \
 	-a $(CONFIG_SPL_TEXT_BASE) -e $(CONFIG_SPL_TEXT_BASE) -n SPL