agx: special case mov_imm

so we can rm a worse special case

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31908>

src/asahi/compiler/agx_opcodes.py

@@ -247,7 +247,6 @@ op("hmul",
 
 op("mov_imm",
       encoding_32 = (0x62, 0xFF, 6, 8),
-      encoding_16 = (0x62, 0xFF, 4, 6),
       imms = [IMM])
 
 op("iadd",

src/asahi/compiler/agx_pack.c

@@ -513,6 +513,9 @@ agx_pack_alu(struct util_dynarray *emission, agx_instr *I)
 
    /* Determine length bit */
    unsigned length = encoding.length_short;
+   if (I->op == AGX_OPCODE_MOV_IMM && I->dest[0].size == AGX_SIZE_16)
+      length -= 2;
+
    uint64_t short_mask = BITFIELD64_MASK(8 * length);
    bool length_bit = (extend || (raw & ~short_mask));