drm/amd/display: make wake_up_aux_channel static

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

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dp.c:5230:16: warning: no previous prototype for function 'wake_up_aux_channel'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2581


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>