target/riscv: Check nanboxed inputs in trans_rvf.inc.c

target/riscv: Check nanboxed inputs in trans_rvf.inc.c

If a 32-bit input is not properly nanboxed, then the input is replaced
with the default qnan.  The only inline expansion is for the sign-changing
set of instructions: FSGNJ.S, FSGNJX.S, FSGNJN.S.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Message-Id: <20200724002807.441147-6-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>