target/riscv: Add multi extension implied rules

target/riscv: Add multi extension implied rules

Add multi extension implied rules to enable the implied extensions of
the multi extension recursively.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Jerry Zhang Jian <jerry.zhangjian@sifive.com>
Tested-by: Max Chou <max.chou@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240625114629.27793-5-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>