[make] rename INCLUDES -> GLOBAL_INCLUDES

To be more consistent, rename make variable INCLUDES to GLOBAL_INCLUDES.
Also remove the need to put -I in front of each field, the make system
will do that for you.

To fix your module makefiles:
-Change INCLUDES -> GLOBAL_INCLUDES
-Remove -I prefix

platform/stellaris/rules.mk

@@ -24,8 +24,8 @@ ifeq ($(MEMSIZE),)
 $(error need to define MEMSIZE)
 endif
 
-INCLUDES += \
-	-I$(LOCAL_DIR)/include \
+GLOBAL_INCLUDES += \
+	$(LOCAL_DIR)/include \
 
 MODULE_SRCS += \
 	$(LOCAL_DIR)/debug.c \

platform/stellaris/ti/rules.mk

@@ -1,6 +1,6 @@
 LOCAL_DIR := $(GET_LOCAL_DIR)
 
-INCLUDES += -I$(LOCAL_DIR)
+GLOBAL_INCLUDES += $(LOCAL_DIR)
 
 MODULE_SRCS += \
 	$(LOCAL_DIR)/driverlib/adc.c \