Support theme width and height offsets

Current use condition is LG V20, where the secondary screen is
actually just a corner chunk of the main screen.
In this case, we need to shift the UI down some pixels in order
to see it all, but just using Y offsets resulted in losing
the rest of the GUI below.

Example in BoardConfig.mk:
  # Shift TWRP off the secondary screen
  TW_Y_OFFSET := 160
  TW_H_OFFSET := -160

Change-Id: I5a06638ba0d05e5b9fd8a6245c630d6ea3394f78
diff --git a/gui/Android.mk b/gui/Android.mk
index b514e5b..dab35a4 100644
--- a/gui/Android.mk
+++ b/gui/Android.mk
@@ -67,6 +67,12 @@
 ifneq ($(TW_Y_OFFSET),)
     LOCAL_CFLAGS += -DTW_Y_OFFSET=$(TW_Y_OFFSET)
 endif
+ifneq ($(TW_W_OFFSET),)
+    LOCAL_CFLAGS += -DTW_W_OFFSET=$(TW_W_OFFSET)
+endif
+ifneq ($(TW_H_OFFSET),)
+    LOCAL_CFLAGS += -DTW_H_OFFSET=$(TW_H_OFFSET)
+endif
 ifeq ($(TW_ROUND_SCREEN), true)
     LOCAL_CFLAGS += -DTW_ROUND_SCREEN
 endif