QemuMacDrivers: update qemu_vga.ndrv to 90c488d built from submodule

This update to qemu_vga.ndrv includes the following changes:

- Build guest resolution list from QEMU EDID data if enabled
- Fixes to re-enable 256 color mode

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

roms/QemuMacDrivers

@@ -1 +1 @@
-Subproject commit d4e7d7ac663fcb55f1b93575445fcbca372f17a7
+Subproject commit 90c488d5f4a407342247b9ea869df1c2d9c8e266