rkflashtool: refactor / improve code readability
rkflashtool: Read NAND Flash ID / Info

cf. FW_ReadID() and FW_GetFlashInfo() in U-Boot (rockusb)

    $ rkflashtool n

    rkflashtool: info: rkflashtool v5.2
    rkflashtool: info: Detected RK3188...
    rkflashtool: info: interface claimed
    rkflashtool: info: Flash ID: 2c 64 44 4b a9
    rkflashtool: info: Flash Info:
            Manufacturer: Micron (value: 4)
            Flash Size: 8192MB
            Block Size: 2048KB
            Page Size: 8KB
            ECC Bits: 40
            Access Time: 32
            Flash CS: Flash<0>