mtd: nand: denali_dt: add a DT driver

A patch for NAND uclass support was proposed about half a year ago:
https://patchwork.ozlabs.org/patch/722282/



It was not merged and I do not see on-going work for this.

Without DM-based probing, we need to set up pinctrl etc. in an ad-hoc
way and give lots of crappy CONFIG options for base addresses and
properties, which are supposed to be specified by DT.  This is painful.

This commit just provides a probe hook to retrieve "reg" from DT and
allocate private data in a DM manner.  This DT driver is not essentially
a NAND driver, in fact it is (ab)using UCLASS_MISC.  Once UCLASS_NAND is
supported, it would be possible to migrate to it.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>