[PATCH 2/3] [MTD] [OneNAND] Add write-while-program support

[Kyungmin Park]

It's similar with read-while-program method.
but it's write side performance improvement.

Here's brief performance results.
Note: Measured from OMAP3 with async OneNAND mode. (not sync mode)

=================================================================
speedtest: dev = 3
speedtest: Size=16777216  EB size=131072  Write size=2048  EB count=128
                Pages per EB=64  Page size=2048
speedtest: scanning for bad blocks
speedtest: scanned 0
speedtest: scanned 128, found 0 bad
speedtest: erasing
speedtest: erased 0
speedtest: erased 128
speedtest: Testing eraseblock write speed
eraseblock write speed is 2592 KiB/s
speedtest: Testing eraseblock read speed
eraseblock read speed is 16786 KiB/s
speedtest: Testing page write speed
page write speed is 2966 KiB/s
speedtest: Testing page read speed
page read speed is 13277 KiB/s
speedtest: Testing 2 page write speed
2 page write speed is 3182 KiB/s
speedtest: Testing 2 page read speed
2 page read speed is 14773 KiB/s
speedtest: Testing erase speed
erase speed is 192752 KiB/s
speedtest: speedtest finished
=================================================================

Also it's passed all nand-tests.