[ARM] pxa/palm: add NAND Flash support for PalmTX

This patch adds support for NAND chip found in PalmTX handheld. Support
is implemented through the gen_nand driver.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>