hw/vmware_vga.c: various vmware vga fixes.

Hardcode depth to 32 bpp.  It effectively was that way before because
that is the default surface depth, this just makes it explicit in the
code.

Rename depth to new_depth to make it consistent with the new_width +
new_height names.  In theory we can make new_depth changeable (i.e.
allow the guest to fill in -- say -- 16 there).  In practice the guests
don't try, the X-Server refuses to start if you ask it to use 16bpp
depth (via DefaultDepth in the Screen section).

Always return the correct rmask+gmask+bmask values for the given
new_depth.

Fix mode setting to also verify at new_depth to make sure we have a
correct DisplaySurface, even if the current video mode happes to be
16bpp (set by vgabios via bochs vbe interface).  While being at it
switch over to use qemu_create_displaysurface_from, so the surface is
backed by guest-visible video memory and we save a memcpy.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
