drm/amd/display: Add missing static

After enable DRM_AMDGPU_WERROR, clang highlight multiple functions that
need to have `static`, and this commit address those issues and also
improve the indents.

Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Acked-by: Alan Liu <haoping.liu@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/amd/display: Adding prototype for dccg21_update_dpp_dto()

Kernel test robot throws below warning ->

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn21/dcn21_dccg.c:46:6:
warning: no previous prototype for 'dccg21_update_dpp_dto'
[-Wmissing-prototypes]

Adding prototype for dccg21_update_dpp_dto().

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drm/amd/display: update dpp dto phase and modulo.

[Why & How]
Program modulo with ref dpp clk Mhz/10.
Program phase with pipe dpp clk Mhz /10.
DMUB FW could use these value to determine optimization clk
for PSR power saving.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>