target/riscv: Restrict mideleg/medeleg/medelegh access to S-mode harts

target/riscv: Restrict mideleg/medeleg/medelegh access to S-mode harts

RISC-V Privileged Spec states:
"In harts with S-mode, the medeleg and mideleg registers must exist, and
setting a bit in medeleg or mideleg will delegate the corresponding trap
, when occurring in S-mode or U-mode, to the S-mode trap handler. In
harts without S-mode, the medeleg and mideleg registers should not
exist."

Add smode predicate to ensure these CSRs are only accessible when S-mode
is supported.

Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Jay Chang <jay.chang@sifive.com>
Reviewed-by: Nutty Liu<liujingqi@lanxincomputing.com>
Message-ID: <20250701030021.99218-2-jay.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>