drm/amd/display: change several dcn201 variables storage-class-specifier to static

smatch reports these similar problems in dcn201
drivers/gpu/drm/amd/amdgpu/../display/dc/clk_mgr/dcn201/dcn201_clk_mgr.c:165:22:
  warning: symbol 'dcn201_funcs' was not declared. Should it be static?
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_resource.c:77:30:
  warning: symbol 'dcn201_ip' was not declared. Should it be static?
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_resource.c:139:37:
  warning: symbol 'dcn201_soc' was not declared. Should it be static?
drivers/gpu/drm/amd/amdgpu/../display/dc/dcn201/dcn201_mpc.c:79:24:
  warning: symbol 'dcn201_mpc_funcs' was not declared. Should it be static?

All of these are only used in their definition file, so they should be static

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>