nandtest: Introduce multiple reads & check iterations

nandtest: Introduce multiple reads & check iterations

The current nandtest performs a simple test which consists of:

  1. erase block
  2. write data
  3. read and verify

In order to improve the nandtest strength, this commit adds a new parameter
to increase the number of "read and verify" iterations. In other words,
the test now consists of:

  1. erase block
  2. write data
  3. read and verify (N times)

This seem to apply more pressure on a NAND driver's ECC engine and has been
used to discover stability problems with an old OMAP2.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>