option to allow recovery to use 24-bit graphics in UI

Add "RECOVERY_24_BIT := true" to the device's BoardConfig.mk to use
24-bit framebuffers in the recovery ui.

Change-Id: Iaede138bf7870becf237f12f1c0e49c9ff82d007
diff --git a/minui/Android.mk b/minui/Android.mk
index 91dd939..7ded5d3 100644
--- a/minui/Android.mk
+++ b/minui/Android.mk
@@ -9,4 +9,8 @@
 
 LOCAL_MODULE := libminui
 
+ifneq ($(RECOVERY_24_BIT),)
+  LOCAL_CFLAGS += -DRECOVERY_24_BIT
+endif
+
 include $(BUILD_STATIC_LIBRARY)