[Yaffs] partitioning yportenv.h

Hi Yaffsers

To sweeten things up with an eye to adding YAFFS to the Linux kernel, I have
split up yportenv.h slightly.

The WinCE stuff now lives in a file called ywinceenv.h in the wince
sub-directory, and likewise the YAFFS direct stuff has been carved off.

Modified: yportenv.h
Added: wince/ywinceenv.h direct/ydirectenv.h

Regards

-- Charles