[Yaffs] New Yaffs driver model

Hello All

It has been a long time coming, but Yaffs now has a new driver model.

The old drivers had to know all about tags and the twists in packing them.

The new driver model refactors all that. Tags handling has been pulled into a
new layer (yaffs_tags_marshall.c) and the drivers just deal with transferring
bytes to/from flash, erasing, and other low-level stuff.

These changes make it far easier to integrate Yaffs. There is no need to learn
all those Yaffs-isms,

Along with the new driver model, Yaffs Direct Interface (the RTOS/portable
version of Yaffs) also has some new example drivers. These new drivers are
real drivers that work with back-end flash simulators and should work with
real hardware with only slight tweaks. That also makes it a lot easier to get
Yaffs up and running on a new platform. There are example drivers for regular
NAND, CFI-style NOR and Intel M18 ( a whacky NOR architecture that is part
SLC and part MLC).


Regards

Charles