drm/amdgpu/display: Address kdoc for 'is_psr_su' in 'fill_dc_dirty_rects'

The is_psr_su parameter is a boolean flag indicating whether the Panel
Self Refresh Selective Update (PSR SU) feature is enabled which is a
power-saving feature that allows only the updated regions of the screen
to be refreshed, reducing the amount of data that needs to be sent to
the display.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:5257: warning: Function parameter or member 'is_psr_su' not described in 'fill_dc_dirty_rects'

Fixes: d16df040 ("drm/amdgpu: make damage clips support configurable")
Cc: stable@vger.kernel.org
Cc: Hamza Mahfooz <hamza.mahfooz@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>