target/riscv: Update MISA.X for non-standard extensions

target/riscv: Update MISA.X for non-standard extensions

MISA.X is set if there are any non-standard extensions.
We should set MISA.X when any of the vendor extensions is enabled.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Max Chou <max.chou@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20260424050509.3935180-3-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>