drm: Implement DRM aperture helpers under video/

drm: Implement DRM aperture helpers under video/

Implement DRM's aperture helpers under video/ for sharing with other
sub-systems. Remove DRM-isms from the interface. The helpers track
the ownership of framebuffer apertures and provide hand-over from
firmware, such as EFI and VESA, to native graphics drivers.

Other subsystems, such as fbdev and vfio, also have to maintain ownership
of framebuffer apertures. Moving DRM's aperture helpers to a more public
location allows all subsystems to interact with each other and share a
common implementation.

The aperture helpers are selected by the various firmware drivers within
DRM and fbdev, and the VGA text-console driver.

The original DRM interface is kept in place for use by DRM drivers.

v3:
	* prefix all interfaces with aperture_ (Javier)
	* rework and simplify documentation (Javier)
	* rename struct dev_aperture to struct aperture_range
	* rebase onto latest DRM
	* update MAINTAINERS entry

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220622140134.12763-3-tzimmermann@suse.de