pan/bi: Add format field to IR

To make register_format packing explicit, and possibly in the future
support the auto mode.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6749>
diff --git a/src/panfrost/bifrost/compiler.h b/src/panfrost/bifrost/compiler.h
index b839156..24d26b2 100644
--- a/src/panfrost/bifrost/compiler.h
+++ b/src/panfrost/bifrost/compiler.h
@@ -286,6 +286,9 @@
         /* Source types if required by the class */
         nir_alu_type src_types[BIR_SRC_COUNT];
 
+        /* register_format if applicable */
+        nir_alu_type format;
+
         /* If the source type is 8-bit or 16-bit such that SIMD is possible,
          * and the class has BI_SWIZZLABLE, this is a swizzle in the usual
          * sense. On non-SIMD instructions, it can be used for component