target/riscv: Implement Smdbltrp behavior

target/riscv: Implement Smdbltrp behavior

When the Smsdbltrp ISA extension is enabled, if a trap happens while
MSTATUS.MDT is already set, it will trigger an abort or an NMI is the
Smrnmi extension is available.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250110125441.3208676-9-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>