drm/amd/display: replace msleep with udelay in fbc path

FBC enabling and disabling path has msleep which leads to
BUG hit when called in atomic context, hence this patch
replaces msleeps with udelays appropriately.

Signed-off-by: Shirish S <shirish.s@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>