yaffs: By default route all writes into the yaffs cache

yaffs: By default route all writes into the yaffs cache

In the past only non-aligned or inband-tags writes were written
into the internal cache. However the cache has some benefits
with certain write patterns, so the default has been changed to
always write into the cache.

A control parameter has been added to bypass the cache for aligned writes.

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