drm/amd: Mark IP_BASE definition as __maybe_unused

Silences 166 compile-time warnings like:

warning: 'UVD0_BASE' defined but not used [-Wunused-const-variable=]
129 | static const struct IP_BASE UVD0_BASE ={ { { { 0x00007800, 0x00007E00, 0, 0, 0 } },
| ^~~~~~~~~
warning: 'UMC0_BASE' defined but not used [-Wunused-const-variable=]
123 | static const struct IP_BASE UMC0_BASE ={ { { { 0x00014000, 0, 0, 0, 0 } },
| ^~~~~~~~~

Signed-off-by: Isabella Basso <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/include/cyan_skillfish_ip_offset.h

···
 #define MAX_SEGMENT                                        5
 
 
-struct IP_BASE_INSTANCE 
+struct IP_BASE_INSTANCE
 {
     unsigned int segment[MAX_SEGMENT];
-};
- 
-struct IP_BASE 
+} __maybe_unused;
+
+struct IP_BASE
 {
     struct IP_BASE_INSTANCE instance[MAX_INSTANCE];
-};
+} __maybe_unused;
 
 
 static const struct IP_BASE ATHUB_BASE            ={ { { { 0x00000C00, 0, 0, 0, 0 } },

drivers/gpu/drm/amd/include/yellow_carp_offset.h

···
 struct IP_BASE_INSTANCE
 {
     unsigned int segment[MAX_SEGMENT];
-};
+} __maybe_unused;
 
 struct IP_BASE
 {
     struct IP_BASE_INSTANCE instance[MAX_INSTANCE];
-};
+} __maybe_unused;
 
 
 static const struct IP_BASE ACP_BASE = { { { { 0x02403800, 0x00480000, 0, 0, 0, 0 } },