drm/amd/display: make configure_lttpr_mode_transparent and...

drm/amd/display: make configure_lttpr_mode_transparent and configure_lttpr_mode_non_transparent static

This symbols is not used outside of dc_link_dp.c, so marks it static.

Fix the following sparse warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c:1766:16:
warning: symbol 'configure_lttpr_mode_non_transparent' was not declared.
Should it be static?

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c:1755:16:
warning: symbol 'configure_lttpr_mode_transparent' was not declared.
Should it be static?

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: chongjiapeng <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>