Optimize instruction fetch (riscv_inst_fetch) to use 32-bit fetches
Optimize instruction fetch (riscv_inst_fetch) to use 32-bit fetches

- Use 32-bit fetch as this is the fast path for a single aligned
  load on aligned 32-bit code. If another instruction size is
  detected (RVC) then either a mask to 16-bits or additional
  fetch to support 2, 4, 6 and 8 byte instructions.

rv8-io/rv8,rv8-io/rv8,rv8-io/rv8