[Yaffs] Current YAFFS2 status

[Martin Fouts]

I've just made my last pre-cleanup checkin.

I've added the patchin script, taken shamelessly from the originaly
YAFFS patchin script, and two files needed by it, Kconfig and
Makefile.kernel.

This means that if you prefer building your yaffs as part of a kernel
make, rather than as a separate module, you can use he patchin script to
set the kernel up to support that.

Marty