misc-utils: flashcp: Add new function that copy only different blocks

misc-utils: flashcp: Add new function that copy only different blocks

- The original flashcp process is erase, write and verify all blocks
  in one time from file to device.
  This patch will add a function that only copy different block data
  from file to device. The function will compare blocks by block
  between file and device, then erase and write block data from file
  to device if found different block.

Signed-off-by: Harvey Wu <harveywu95@gmail.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>