drm/amd/pm/powerplay/smumgr/smu9_smumgr: Include our own header containing our prototypes

drm/amd/pm/powerplay/smumgr/smu9_smumgr: Include our own header containing our prototypes

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

 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/smumgr/smu9_smumgr.c:38:6: warning: no previous prototype for ‘smu9_is_smc_ram_running’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/smumgr/smu9_smumgr.c:112:5: warning: no previous prototype for ‘smu9_send_msg_to_smc’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/smumgr/smu9_smumgr.c:140:5: warning: no previous prototype for ‘smu9_send_msg_to_smc_with_parameter’ [-Wmissing-prototypes]
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/smumgr/smu9_smumgr.c:165:10: warning: no previous prototype for ‘smu9_get_argument’ [-Wmissing-prototypes]

Cc: Evan Quan <evan.quan@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>