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>

target/riscv/internals.h

@@ -43,6 +43,7 @@ enum {
     RISCV_FRM_RUP = 3,  /* Round Up */
     RISCV_FRM_RMM = 4,  /* Round to Nearest, ties to Max Magnitude */
     RISCV_FRM_DYN = 7,  /* Dynamic rounding mode */
+    RISCV_FRM_ROD = 8,  /* Round to Odd */
 };
 
 static inline uint64_t nanbox_s(float32 f)