riscv: Add SiFive xsfvqmaccdod and xsfvqmaccqoq vendor extensions

Add SiFive vendor extension support to the kernel with the target of
"xsfvqmaccdod" and "xsfvqmaccqoq".

Signed-off-by: Cyan Yang <cyan.yang@sifive.com>
Link: https://lore.kernel.org/r/20250418053239.4351-3-cyan.yang@sifive.com


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