drm/ast: Remove unused code paths for AST 1180

drm/ast: Remove unused code paths for AST 1180

[ Upstream commit 05f13f5b5996d20a9819e0c6fd0cda4956c8aff9 ]

The ast driver contains code paths for AST 1180 chips. The chip is not
supported and the rsp code has never been tested. Simplify the driver by
removing the AST 1180 code.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200617080340.29584-2-tzimmermann@suse.de
Signed-off-by: Sasha Levin <sashal@kernel.org>