drm/amd/display: Add new set_fc_enable to struct dwbc_funcs

[WHAT]
Add a function to enable and disable DWB's frame captures.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>