fbdev: Simplify fb_is_primary_device for x86

fbdev: Simplify fb_is_primary_device for x86

vga_default_device really is supposed to cover all corners, at least
for x86. Additionally checking for rom shadowing should be redundant,
because the bios/fw only does that for the boot vga device.

If this turns out to be wrong, then most likely that's a special case
which should be added to the vgaarb code, not replicated all over.

Patch motived by changes to the aperture helpers, which also have this
open code in a bunch of places, and which are all removed in a
clean-up series. This function here is just for selecting the default
fbdev device for fbcon, but I figured for consistency it might be good
to throw this patch in on top.

Note that the shadow rom check predates vgaarb, which was only wired
up in commit 88674088d10c ("x86: Use vga_default_device() when
determining whether an fb is primary"). That patch doesn't explain why
we still fall back to the shadow rom check.

v4:
- fix commit message style (i.e., commit 1234 ("..."))
- fix Daniel's S-o-b address

v5:
- add back an S-o-b tag with Daniel's Intel address

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230406132109.32050-9-tzimmermann@suse.de