android: Define Make variables for Android version

Define the following Make variables:
    MESA_ANDROID_MAJOR_VERSION
    MESA_ANDROID_MINOR_VERSION
    MESA_ANDROID_VERSION

These variable will allow us to make version-dependent decisions on
library dependencies. In particular, building Mesa against JellyBean will
require libsync.

Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
diff --git a/Android.common.mk b/Android.common.mk
index 18e5726..d0a5f1a 100644
--- a/Android.common.mk
+++ b/Android.common.mk
@@ -34,10 +34,8 @@
 	$(MESA_TOP)/include
 
 # define ANDROID_VERSION (e.g., 4.0.x => 0x0400)
-major := $(word 1, $(subst ., , $(PLATFORM_VERSION)))
-minor := $(word 2, $(subst ., , $(PLATFORM_VERSION)))
 LOCAL_CFLAGS += \
-	-DANDROID_VERSION=0x0$(major)0$(minor)
+	-DANDROID_VERSION=0x0$(MESA_ANDROID_MAJOR_VERSION)0$(MESA_ANDROID_MINOR_VERSION)
 
 LOCAL_CFLAGS += \
 	-DHAVE_PTHREAD=1 \