DRM: Add a new 'boot_display' attribute

DRM: Add a new 'boot_display' attribute

On systems with multiple GPUs there can be uncertainty which GPU is the
primary one used to drive the display at bootup. In some desktop
environments this can lead to increased power consumption because
secondary GPUs may be used for rendering and never go to a low power
state. In order to disambiguate this add a new sysfs attribute
'boot_display' that uses the output of video_is_primary_device() to
populate whether the PCI device was used for driving the display.

Suggested-by: Manivannan Sadhasivam <mani@kernel.org>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/issues/23
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250811162606.587759-5-superm1@kernel.org
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>