target/riscv: Add Zicfilp support for Smrnmi

target/riscv: Add Zicfilp support for Smrnmi

Zicfilp extension introduces the MNPELP (bit 9) in mnstatus.
The MNPELP field holds the previous ELP.

When a RNMI trap is delivered, the MNPELP is set to ELP and ELP set
to NO_LP_EXPECTED. Upon a mnret, if the mnstatus.MNPP holds the
value y, then ELP is set to the value of MNPELP if yLPE is 1;
otherwise, it is set to NO_LP_EXPECTED.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250106054336.1878291-7-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>