sdl: Add QEMU mascot icon for use with SDL

sdl: Add QEMU mascot icon for use with SDL

This is a bitmap file (32x32x4) derived from the official QEMU mascot
(which was designed by Benoît Canet). I stripped the text from the SVG
to get a nearly square image and converted the result to BMP without
any manual optimization.

The bitmap is currently used by QEMU's SDL interface and replaces the
default X icon.

v2: Add qemu-icon.bmp to Makefile.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>