Improve memory read/write

[qwe661234]

After analyzing the data collected during the execution of the dhrystone benchmark, it becomes evident that the primary performance bottleneck lies in memory read and write operations. To address this issue and improve performance, we should consider modifying the implementation of these memory operations.

  21.15%  rv32emu  rv32emu           [.] memory_write
  17.21%  rv32emu  rv32emu           [.] do_sw
  12.82%  rv32emu  rv32emu           [.] do_lw
   6.89%  rv32emu  rv32emu           [.] memory_read_w
   6.68%  rv32emu  rv32emu           [.] on_mem_write_w

[jserv]

semu.c applies the technique Duff's device to generalize memory operations. See ram_load and ram_store.
We may eliminate unnecessary range checks for memory chunks. Furthermore, memory chunk in src/io.c is not really vital for implementing RV32 emulation though.