mtd: nand: pxa3xx: Switch FIFO draining to jiffies-based timeout

Now that the driver handles the FIFO draining in a threaded interrupt, we can
base our timeout on jiffies and sleeping, instead of using mdelay.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>