macfb: use memory_region_init_ram() in macfb_common_realize() for the framebuffer

macfb: use memory_region_init_ram() in macfb_common_realize() for the framebuffer

Currently macfb_common_realize() defines the framebuffer RAM memory region as
being non-migrateable but then immediately registers it for migration. Replace
memory_region_init_ram_nomigrate() with memory_region_init_ram() which is clearer
and does exactly the same thing.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20211007221253.29024-6-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>