target/riscv: add shvstvecd

target/riscv: add shvstvecd

shvstvecd is defined in RVA22 as:

"vstvec.MODE must be capable of holding the value 0 (Direct).
When vstvec.MODE=Direct, vstvec.BASE must be capable of holding any
valid four-byte-aligned address."

This is always true for TCG so let's claim support for it.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241218114026.1652352-7-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>