target/riscv: add "set round to odd" rounding mode helper function

target/riscv: add "set round to odd" rounding mode helper function

helper_set_rounding_mode() is responsible for SIGILL, and "round to odd"
should be an interface private to translation, so add a new independent
helper_set_rod_rounding_mode().

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-64-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>