[PATCH]: cmd: part: add part block command

[razvan.becheriu at gmail.com <razvan.becheriu@gmail.com>]

    The Intel Edison OTA process requires a conversion of data size
    from bytes to number of blocks. The following functions are used:

    # function ota_conv_sizes
    # Convert a bytes size to a block size
    # input  bytesize : size in bytes to convert
    # input  blksize  : size of a block in bytes
    # output num_blk  : converted size in blocks

    # function ota_mmc_write
    # Write a memory buffer to mmc drive
    # input floadaddr    : address of buffer to write
    # input u_part_start : block start in mmc
    # input num_blk      : number of block to write

    This patch adds the cmd part sub-command 'block' which returns
    the partition block size in bytes.