target/riscv: Add check for 16-bit aligned PC for different priv versions.

target/riscv: Add check for 16-bit aligned PC for different priv versions.

For privilege version 1.12 or newer, C always implies Zca. We can only
check ext_zca to allow 16-bit aligned PC addresses. For older privilege
versions, we only check C.

Signed-off-by: Yu-Ming Chang <yumin686@andestech.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <174184718265.10540.10120024221661781046-0@git.sr.ht>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>