arm: mach-keystone: config.mk: Adds support for secure, images on 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.

---

Changes in v3:
- Corrects commit message in patch 5/7 in this series to refer to u-boot_HS_MLO

Changes in v2:
- Changes the target for secure keystone devices in config.mk to u-boot_HS_MLO to keep it in line with the MLO target that is built for non-secure keystone devices.

  arch/arm/mach-keystone/config.mk | 6 ++++++
  1 file changed, 6 insertions(+)

b/arch/arm/mach-keystone/config.mk
index 9ae1e9a..32fef42 100644

@@ -5,9 +5,15 @@
  # SPDX-License-Identifier:     GPL-2.0+
  #
 
+include  $(srctree)/$(CPUDIR)/omap-common/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

2.7.4