drm/bochs: fix blanking

drm/bochs: fix blanking

[ Upstream commit e740ceb53e4579a7a4063712cebecac3c343b189 ]

VGA_IS1_RC is the color mode register (VGA_IS1_RM the one for monochrome
mode, note C vs. M at the end).  So when using VGA_IS1_RC make sure the
vga device is actually in color mode and set the corresponding bit in the
misc register.

Reproducible when booting VMs in UEFI mode with some edk2 versions (edk2
fix is on the way too).  Doesn't happen in BIOS mode because in that
case the vgabios already flips the bit.

Fixes: 250e743915d4 ("drm/bochs: Add screen blanking support")
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20220906142957.2763577-1-kraxel@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>