RISC-V implementation source mixes tabs with spaces

[phillipstanleymarbell]

RISC-V implementation source mixes tabs with spaces (or uses spaces instead of tabs) in several files:

• decode-riscv.c
• decode-riscv.h
• instr-riscv.h
• machine-riscv.c
• opstr-riscv.h (stray space right after each ']' before the tab)

(cc: @Z-Gu)