android: intel: Flatten the makefile structure

Android porting of commit bebc1a1 "intel: Flatten the makefile structure"

Automake approach was followed, by moving makefiles a level up,
naming them Android.genxml.mk and Android.isl.mk,
performing the necessary adjustments to the paths,
adding src/intel/Android.mk and fixing mesa top level makefile.

Acked-by: Jason Ekstrand <jason@jlekstrand.net>
diff --git a/Android.mk b/Android.mk
index a83cb33..dfc45c4 100644
--- a/Android.mk
+++ b/Android.mk
@@ -95,8 +95,7 @@
 	src/mesa \
 	src/util \
 	src/egl \
-	src/intel/genxml \
-	src/intel/isl \
+	src/intel \
 	src/mesa/drivers/dri
 
 INC_DIRS := $(call all-named-subdir-makefiles,$(SUBDIRS))