riscv: csr: Add CSR encodings for CSR_VXRM/CSR_VXSAT

The VXRM vector csr for xtheadvector has an encoding of 0xa and VXSAT
has an encoding of 0x9.

Co-developed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Yangyu Chen <cyy@cyyself.name>
Link: https://lore.kernel.org/r/20241113-xtheadvector-v11-7-236c22791ef9@rivosinc.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>