target/riscv: Add Ssdbltrp CSRs handling

target/riscv: Add Ssdbltrp CSRs handling

Add ext_ssdbltrp in RISCVCPUConfig and implement MSTATUS.SDT,
{H|M}ENVCFG.DTE and modify the availability of MTVAL2 based on the
presence of the Ssdbltrp ISA extension.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250110125441.3208676-3-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>