vga16fb: drop powerpc support

vga16fb: drop powerpc support

I noticed that commit 0db5b61e0dc07 ("fbdev/vga16fb: Create
EGA/VGA devices in sysfb code") broke vga16fb on non-x86 platforms,
because the sysfb code never creates a vga-framebuffer device when
screen_info.orig_video_isVGA is set to '1' instead of VIDEO_TYPE_VGAC.

However, it turns out that the only architecture that has allowed
building vga16fb in the past 20 years is powerpc, and this only worked
on two 32-bit platforms and never on 64-bit powerpc. The last machine
that actually used this was removed in linux-3.10, so this is all dead
code and can be removed.

The big-endian support in vga16fb.c could also be removed, but I'd just
leave this in place.

Fixes: 933ee7119fb14 ("powerpc: remove PReP platform")
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Helge Deller <deller@gmx.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231009211845.3136536-8-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>