MIPS support to *.mk files and envsetup.sh

Change-Id: Iba4d046e3202524b29cfe32980927f8cc0aa8496
Signed-off-by: Chris Dearman <chris@mips.com>
Signed-off-by: Raghu Gandham <raghu@mips.com>
diff --git a/core/config.mk b/core/config.mk
index b0b5082..03e4245 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -148,6 +148,9 @@
   $(error Multiple board config files for TARGET_DEVICE $(TARGET_DEVICE): $(board_config_mk))
 endif
 include $(board_config_mk)
+ifeq ($(TARGET_ARCH),)
+  $(error TARGET_ARCH not defined by board config: $(board_config_mk))
+endif
 TARGET_DEVICE_DIR := $(patsubst %/,%,$(dir $(board_config_mk)))
 board_config_mk :=