This reverts commit a896f870.

It causes odd flickering on my Radeon RX580 (PCI ID 1002:67df rev e7,
subsystem ID 1da2:e353).

Bisected right to this commit, and reverting it fixes things.

Link: https://lore.kernel.org/all/CAHk-=wg9hDde_L3bK9tAfdJ4N=TJJ+SjO3ZDONqH5=bVoy_Mzg@mail.gmail.com/
Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Jun Lei <Jun.Lei@amd.com>
Cc: Mustapha Ghaddar <mustapha.ghaddar@amd.com>
Cc: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Cc: meenakshikumar somasundaram <meenakshikumar.somasundaram@amd.com>
Cc: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>