Add support for 32-bit framebuffers.

This modifies the emulator so support 32-bit framebuffers.
You can create such a frame-buffer using one of these methods:

- Add a "bpp 32" line to the "display" element of your skin
- Use the new 'magic' skin option format: e.g. -skin 320x480x32

Note that the result will be hideous since the kernel driver still
thinks the hardware is only 16-bits. This will be addressed in a
later patch to hw/goldfish_fb.c and to the kernel driver
($KERNEL/drivers/video/goldfishfb.c)

Change-Id: I0fc700c4a4cb8521076605324e15ed34e5d01136
diff --git a/framebuffer.h b/framebuffer.h
index 0e502d1..7a69440 100644
--- a/framebuffer.h
+++ b/framebuffer.h
@@ -40,6 +40,7 @@
 typedef enum {
     QFRAME_BUFFER_NONE   = 0,
     QFRAME_BUFFER_RGB565 = 1,
+    QFRAME_BUFFER_RGBX_8888 = 2,
     QFRAME_BUFFER_MAX          /* do not remove */
 } QFrameBufferFormat;