gpu: nova-core: expose the offset of each register as a type constant

Although we want to access registers using the provided methods, it is
sometimes needed to use their raw offset, for instance when working with
a register array.

Expose the offset of each register using a type constant to avoid
resorting to hardcoded values.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250619-nova-frts-v6-8-ecf41ef99252@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Author: Gnurou

drivers/gpu/nova-core/regs/macros.rs

@@ -78,7 +78,7 @@ macro_rules! register {
             $($fields:tt)*
         }
     ) => {
-        register!(@common $name $(, $comment)?);
+        register!(@common $name @ $offset $(, $comment)?);
         register!(@field_accessors $name { $($fields)* });
         register!(@io $name @ $offset);
     };
@@ -89,7 +89,7 @@ macro_rules! register {
             $($fields:tt)*
         }
     ) => {
-        register!(@common $name $(, $comment)?);
+        register!(@common $name @ $offset $(, $comment)?);
         register!(@field_accessors $name { $($fields)* });
         register!(@io$name @ + $offset);
     };
@@ -98,14 +98,19 @@ macro_rules! register {
 
     // Defines the wrapper `$name` type, as well as its relevant implementations (`Debug`, `BitOr`,
     // and conversion to regular `u32`).
-    (@common $name:ident $(, $comment:literal)?) => {
+    (@common $name:ident @ $offset:literal $(, $comment:literal)?) => {
         $(
         #[doc=$comment]
         )?
         #[repr(transparent)]
         #[derive(Clone, Copy, Default)]
         pub(crate) struct $name(u32);
 
+        #[allow(dead_code)]
+        impl $name {
+            pub(crate) const OFFSET: usize = $offset;
+        }
+
         // TODO: display the raw hex value, then the value of all the fields. This requires
         // matching the fields, which will complexify the syntax considerably...
         impl ::core::fmt::Debug for $name {