drm/amd/display: make mpc32_program_shaper and mpc32_program_3dlut static

These two functions are not used outside the function dcn32_mpc.c, so the
modification is defined as static.

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn32/dcn32_mpc.c:704:6: warning: no previous prototype for ‘mpc32_program_shaper’.
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn32/dcn32_mpc.c:900:6: warning: no previous prototype for ‘mpc32_program_3dlut’.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2115


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