ir3: Don't consider r63.x as a GPR

We have to be careful here because r63.x is also used to mean "register
not assigned yet," but dummy destinations for prefetches will use r63.x
and we don't want them to count as GPRs when determining whether to
enable early preamble.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29873>

src/freedreno/ir3/ir3.h

@@ -1369,6 +1369,9 @@ is_reg_gpr(const struct ir3_register *reg)
 {
    if ((reg_num(reg) == REG_A0) || (reg->flags & IR3_REG_PREDICATE))
       return false;
+   if (!(reg->flags & (IR3_REG_SSA | IR3_REG_RELATIV)) &&
+       reg->num == INVALID_REG)
+      return false;
    return true;
 }