fix(asm): materialise RISC-V MOV immediates

testdata/verify/movimm_riscv64.s

@@ -0,0 +1,19 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "textflag.h"
+
+TEXT ·movimm(SB), NOSPLIT, $0
+	MOV $0, X10
+	MOV $5, X10
+	MOV $42, X10
+	MOV $-1, X10
+	MOV $-2048, X10
+	MOV $-2049, X10
+	MOV $2047, X10
+	MOV $2048, X10
+	MOV $4095, X10
+	MOV $-4096, X10
+	MOV $0x12345, X10
+	MOV $2147483647, X10
+	RET