riscv64-tok.h: update with more instructions from the spec

riscv64-tok.h: update with more instructions from the spec

defined tokens for C, M, Ziscr extensions.

separate the base RV32 instructions from the RV64, for potential future
re-use in a RV32-only assembler, from which the RV64-tok can #include

scall, sbreak have been renamed (page 7 of spec),
necessitating some renaming in riscv64-asm.c

riscv-spec-20191213.pdf was used,
in which the "V" extension is not yet ratified.
available under https://riscv.org/technical/specifications/

Tables 16.5–16.7 do not list any "scall"
neither does the privileged spec

3 additional tokens not present in the tables were removed

note that this riscv64-asm.c still contains defects, which will
be addressed in another commit