target/riscv: update mstatus.SD when FS is set dirty

target/riscv: update mstatus.SD when FS is set dirty

remove the check becuase SD bit should summarize FS and XS fields
unconditionally.

Signed-off-by: ShihPo Hung <shihpo.hung@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
(cherry picked from commit 82f014671cf057de51c4a577c9e2ad637dcec6f9)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>