mtd: nand: omap_gpmc: Always use ready/busy pin

mtd: nand: omap_gpmc: Always use ready/busy pin

The functions to detect the state of the ready / busy signal is already
available but only used in the SPL case. Lets use it always, also for the
main U-Boot. As all boards should have this HW connection.

Testing on Siemens Draco (am335x) showed a small perfomance gain by using
this ready pin to detect the NAND chip state. Here the values tested on
Draco with Hynix 4GBit NAND:

Without NAND ready pin:

U-Boot# time nand read 80400000 0 400000

NAND read: device 0 offset 0x0, size 0x400000
4194304 bytes read: OK

time: 2.947 seconds, 2947 ticks

With NAND ready pin:

U-Boot# time nand read 80400000 0 400000

NAND read: device 0 offset 0x0, size 0x400000
4194304 bytes read: OK

time: 2.795 seconds, 2795 ticks

So an increase of approx. 5%.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Roger Meier <r.meier@siemens.com>
Cc: Samuel Egli <samuel.egli@siemens.com>