drm/ast: Fix long time waiting on s3/s4 resume

In resume, DP's launch function, ast_dp_launch, could wait at most 30
seconds before timeout to check if DP is enabled. It could lead to 'DPM
device timeout' and trigger unrecoverable kernel panic.

To avoid this problem, we check if DP enable or not at driver probe only.

Reported-and-tested-by: Wendy Wang <wendy.wang@intel.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217278


Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230530041240.13427-1-jammy_huang@aspeedtech.com