pan/bi: Use canonical name for FAU RAM sources

The uniform_constant field and BIFROST_SRC_CONST_{LO,HI} definitions
seem to imply that those only deal with embedded constants. Let's
rename them to reflect the fact that they actually encode accesses to
the Fast-Access-Uniform RAM.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7151>
diff --git a/src/panfrost/bifrost/compiler.h b/src/panfrost/bifrost/compiler.h
index 7b58d09..bfc58ae 100644
--- a/src/panfrost/bifrost/compiler.h
+++ b/src/panfrost/bifrost/compiler.h
@@ -356,8 +356,8 @@
         /* Configuration for slots 2/3 */
         struct bifrost_reg_ctrl_23 slot23;
 
-        /* Packed uniform/constant */
-        uint8_t uniform_constant;
+        /* Fast-Access-Uniform RAM index */
+        uint8_t fau_idx;
 
         /* Whether writes are actually for the last instruction */
         bool first_instruction;
@@ -369,6 +369,7 @@
  */
 
 typedef struct {
+        uint8_t fau_idx;
         bi_registers regs;
         bi_instruction *fma;
         bi_instruction *add;