Revert "drm/mgag200: Add vblank support"

This reverts commit 6c9e14ee.
This reverts commit d5070c9b.
This reverts commit 89c6ea20.

The VLINE interrupt doesn't work correctly on G200SE-A (at least). We
have also seen missing interrupts on G200ER. So revert vblank support.
Fixes frozen displays and warnings about missed vblanks.

[   33.818362] [CRTC:34:crtc-0] vblank wait timed out

From the vblank code, the driver only keeps the register constants and
the line that disables all interrupts in mgag200_device_init(). Both
is still useful without vblank handling.

Reported-by: Tony Luck <tony.luck@intel.com>
Closes: https://lore.kernel.org/dri-devel/Zvx6lSi7oq5xvTZb@agluck-desk3.sc.intel.com/raw


Tested-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241015063932.8620-1-tzimmermann@suse.de