efifb: Ensure graphics device for efifb stays at PCI D0

We are seeing root ports on some desktop boards support D3cold for
discrete graphics card. So when efifb is in use while graphics device
isn't bound to a driver, PCI and ACPI will put the graphics to D3cold
when runtime suspend kicks in, makes efifb stop working.

So ensure the graphics device won't be runtime suspended, to keep efifb
work all the time.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210129084327.986630-1-kai.heng.feng@canonical.com