Add unratified Smpmpind Smcfiss Smucfiss

[ved-rivos]

Spec: https://github.com/ved-rivos/riscv-isa-manual/blob/smpmpss/src/smcfiss.adoc
PoC: https://github.com/ved-rivos/opensbi/tree/smcfiss

$ cd opensbi
$ make PLATFORM=generic
$ spike --isa=rv64gc_zimop_zcmop_zaamo_zicfiss_zicfilp_smcsrind_smpmpind_smcfiss_smucfiss \
              --priv=mu \
              build/platform/generic/firmware/fw_payload.elf

Needs Zicfiss/Zicfilp enabled toolchain to build opensbi.

$ git clone git@github.com:sifive/riscv-gnu-toolchain.git -b cfi-dev
$ riscv-gnu-toolchain/configure --prefix=<path-to-where-to-build> \
       --with-arch=rv64gc_zicfilp_zicfiss --enable-linux --disable-gdb  \
       --with-extra-multilib-test="rv64gc_zicfilp_zicfiss-lp64d:-static"
$ make -j$(nproc)

encoding.h was hand edited as CSR numbers and new field positions are not yet assigned.

RFC only; not requesting to be merged.

[aswaterman]

LGTM overall. I recommend changing the PR to Draft status until you think it should be considered for merging (which, of course, presupposes that encoding.h has been auto-generated).