tegra: nand: make ONFI detection work

Add the missing bits to the Tegra NAND driver to make ONFI detection work
properly.

Also add it to the Tegra default config, as it seems to be a reasonable thing
to have it available on all boards that use any kind of NAND.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>