agx: Handle uniforms passed to COLLECT

It's useful to be able to copyprop uniform registers into COLLECT. That
requires handling of uniform registers in the parallel copy lowering,
which isn't too hard to add.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18813>

src/asahi/compiler/agx_compiler.h

@@ -769,8 +769,9 @@ struct agx_copy {
    /* Base register destination of the copy */
    unsigned dest;
 
-   /* Base register source of the copy */
+   /* Base register source (or uniform base) of the copy */
    unsigned src;
+   bool is_uniform;
 
    /* Size of the copy */
    enum agx_size size;