target/arm: Diagnose UNALLOCATED in disas_simd_two_reg_misc_fp16

This fprintf+assert has been in place since the beginning.
It is prior to the fp_access_check, so we're still good to
raise sigill here.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/381
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210604183506.916654-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/translate-a64.c

@@ -13234,8 +13234,8 @@ static void disas_simd_two_reg_misc_fp16(DisasContext *s, uint32_t insn)
     case 0x7f: /* FSQRT (vector) */
         break;
     default:
-        fprintf(stderr, "%s: insn 0x%04x fpop 0x%2x\n", __func__, insn, fpop);
-        g_assert_not_reached();
+        unallocated_encoding(s);
+        return;
     }