drm/amd/display/dc/dce110/dce110_mem_input_v: Make local functions static

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:471:6: warning: no previous prototype for ‘dce_mem_input_v_is_surface_pending’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:486:6: warning: no previous prototype for ‘dce_mem_input_v_program_surface_flip_and_addr’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:563:6: warning: no previous prototype for ‘dce_mem_input_v_program_pte_vm’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:636:6: warning: no previous prototype for ‘dce_mem_input_v_program_surface_config’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:922:6: warning: no previous prototype for ‘dce_mem_input_v_program_display_marks’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:945:6: warning: no previous prototype for ‘dce_mem_input_program_chroma_display_marks’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:966:6: warning: no previous prototype for ‘dce110_allocate_mem_input_v’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.c:1008:6: warning: no previous prototype for ‘dce110_free_mem_input_v’ [-Wmissing-prototypes]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>