drm/radeon/cik: Move 'si_*()'s prototypes to shared header

drm/radeon/cik: Move 'si_*()'s prototypes to shared header

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

 drivers/gpu/drm/radeon/si.c:4186:6: warning: no previous prototype for ‘si_vram_gtt_location’ [-Wmissing-prototypes]
 4186 | void si_vram_gtt_location(struct radeon_device *rdev,
 | ^~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/si.c:5186:6: warning: no previous prototype for ‘si_init_uvd_internal_cg’ [-Wmissing-prototypes]
 5186 | void si_init_uvd_internal_cg(struct radeon_device *rdev)
 | ^~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/si.c:5801:6: warning: no previous prototype for ‘si_rlc_reset’ [-Wmissing-prototypes]
 5801 | void si_rlc_reset(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: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>