drm/radeon/sumo_dpm: Move 'sumo_get_pi()'s prototype into shared header

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

 drivers/gpu/drm/radeon/sumo_dpm.c:81:25: warning: no previous prototype for ‘sumo_get_pi’ [-Wmissing-prototypes]
 81 | struct sumo_power_info *sumo_get_pi(struct radeon_device *rdev)
 | ^~~~~~~~~~~

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>

drivers/gpu/drm/radeon/sumo_dpm.h

@@ -207,6 +207,7 @@ u32 sumo_get_sleep_divider_from_id(u32 id);
 u32 sumo_get_sleep_divider_id_from_clock(struct radeon_device *rdev,
 					 u32 sclk,
 					 u32 min_sclk_in_sr);
+struct sumo_power_info *sumo_get_pi(struct radeon_device *rdev);
 
 /* sumo_smc.c */
 void sumo_initialize_m3_arb(struct radeon_device *rdev);

drivers/gpu/drm/radeon/sumo_smc.c

@@ -30,8 +30,6 @@
 #define SUMO_SMU_SERVICE_ROUTINE_ALTVDDNB_NOTIFY  27
 #define SUMO_SMU_SERVICE_ROUTINE_GFX_SRV_ID_20  20
 
-struct sumo_power_info *sumo_get_pi(struct radeon_device *rdev);
-
 static void sumo_send_msg_to_smu(struct radeon_device *rdev, u32 id)
 {
 	u32 gfx_int_req;