Add wait flags to support board/chip specific delays

The NAND flash on the TQM8548_BE modules requires a short delay after
running the UPM pattern like the MPC8360ERDK board does. The TQM8548_BE
requires a further short delay after writing out a buffer. Normally the
R/B pin should be checked, but it's not connected on the TQM8548_BE.
The corresponding Linux FSL UPM driver uses similar delay points at the
same locations. To manage these extra delays in a more general way, I
introduced the "wait_flags" field allowing the board-specific driver to
specify various types of extra delay.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>