NAND: fixes

[Maxim Levitsky]

This is part of my patcheset that touches the nand subsystem

Stanley, patch #2 should now cover attempts to write outside the oob.

Also I did another (don't know if less or more evil) approach to bad block testing.
Now check_bad always takes the controller locks and selects the chip. Thus it is
possible to use read_oob/write_oob.
This however changes behavier of the nand_erase_nand to deny erases if any block within
the range is bad. Also it selects/releases the chip once per erase block.
This is done in patch #5. Patch #6 is ported to that change.

Patches 1-3 are pure fixes.

Best regards,
	Maxim Levitsky