x86/video: Only fall back to vga_default_device() without screen info

x86/video: Only fall back to vga_default_device() without screen info

Some multi GPU systems may have a VGA compatible device, but that might not be
used for display.  If due to enumeration order this device is found before the
one actually used for display then multiple devices may show the boot_display
attribute, confusing userspace.

When screen info is valid, use it exclusively to find the primary device so
that only the device backing the framebuffer is reported.  Only when no
framebuffer has been set up does it make sense to fall back to the default VGA
device.  This ensures at most one primary graphics device, preferably the one
with the framebuffer.

Fixes: ad90860bd10ee ("fbcon: Use screen info to find primary device")
Closes: https://lore.kernel.org/linux-pci/20260618081803.2790848-1-aaron.ma@canonical.com/#t
Reported-by: Aaron Ma <aaron.ma@canonical.com>
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Aaron Ma <aaron.ma@canonical.com>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260623141505.1816786-1-mario.limonciello@amd.com