yaffs Refactor yaffs direct device list management, add nand abstraction, divide...

This all makes for a far cleaner layout of test code.

The new yaffs direct list management allows partitions to be added synamically rather than
statically. This is better for OSs that install partitions at runtime (eg. WInCE).

The nand abstraction makes it tidier to add a new nand driver to yaffs direct and test code.

The test code has been repartitioned to make porting and file management cleaner.

Signed-off-by: Charles Manning <cdhmanning@gmail.com>