pixelflinger: make self-contained

pixelflinger should not be used for new projects and should be moved out
of system/core at some point.  As the first step, move all its headers
under system/core/libpixelflinger/include and update its Android.mk
files so they're not referring to the absolute system/core path anymore.

Change-Id: Idead273ab2c0450409d770f5402c4dba916192a9
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/libpixelflinger/Android.mk b/libpixelflinger/Android.mk
index aa614bc..697db25 100644
--- a/libpixelflinger/Android.mk
+++ b/libpixelflinger/Android.mk
@@ -62,6 +62,8 @@
 LOCAL_SRC_FILES_arm64 := $(PIXELFLINGER_SRC_FILES_arm64)
 LOCAL_SRC_FILES_mips := $(PIXELFLINGER_SRC_FILES_mips)
 LOCAL_CFLAGS := $(PIXELFLINGER_CFLAGS)
+LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
+LOCAL_C_INCLUDES += $(LOCAL_EXPORT_C_INCLUDE_DIRS)
 LOCAL_SHARED_LIBRARIES := libcutils liblog
 
 # Really this should go away entirely or at least not depend on