drm/amd/include/arct_ip_offset: Mark top-level IP_BASE definition as __maybe_unused

drm/amd/include/arct_ip_offset: Mark top-level IP_BASE definition as __maybe_unused

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

 In file included from drivers/gpu/drm/amd/amdgpu/arct_reg_init.c:27:
 drivers/gpu/drm/amd/amdgpu/../include/arct_ip_offset.h:227:29: warning: ‘DBGU_IO_BASE’ defined but not used [-Wunused-const-variable=]
 227 | static const struct IP_BASE DBGU_IO_BASE ={ { { { 0x000001E0, 0x000125A0, 0x0040B400, 0, 0, 0 } },
 | ^~~~~~~~~~~~
 drivers/gpu/drm/amd/amdgpu/../include/arct_ip_offset.h:127:29: warning: ‘PCIE0_BASE’ defined but not used [-Wunused-const-variable=]
 127 | static const struct IP_BASE PCIE0_BASE ={ { { { 0x000128C0, 0x00411800, 0x04440000, 0, 0, 0 } },
 | ^~~~~~~~~~
 In file included from drivers/gpu/drm/amd/amdgpu/arct_reg_init.c:27:
 drivers/gpu/drm/amd/amdgpu/../include/arct_ip_offset.h:63:29: warning: ‘FUSE_BASE’ defined but not used [-Wunused-const-variable=]
 63 | static const struct IP_BASE FUSE_BASE ={ { { { 0x000120A0, 0x00017400, 0x00401400, 0, 0, 0 } },
 | ^~~~~~~~~

Acked-by: Christian König <christian.koenig@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>