agx: Add p_split pseudoinstruction

Easier on RA for extracts.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16268>

src/asahi/compiler/agx_compiler.h

@@ -217,7 +217,7 @@ agx_is_equiv(agx_index left, agx_index right)
    return (left.type == right.type) && (left.value == right.value);
 }
 
-#define AGX_MAX_DESTS 1
+#define AGX_MAX_DESTS 4
 #define AGX_MAX_SRCS 5
 
 enum agx_icond {

src/asahi/compiler/agx_opcodes.py

@@ -253,4 +253,5 @@ op("and", _, srcs = 2)
 op("or", _, srcs = 2)
 
 op("p_combine", _, srcs = 4)
+op("p_split", _, srcs = 1, dests = 4)
 op("p_extract", _, srcs = 1, imms = [COMPONENT])