MFP4 217312, 222008, 222052, 222053, 222673, 231484, 231491, 231565, 570643

Rework the timeout code to use actual time rather than a DELAY() loop and
to use both typical and maximum to allow logging of timeout failures.
Also correct the erase timeout, it is specified in milliseconds not
microseconds like the other timeouts.  Do not invoke DELAY() between
status queries as this adds significant latency which in turn reduced
write performance substantially.

Sanity check timeout values from the hardware.

Implement support for buffered writes (only enabled on Intel/Sharp parts
for now).  This yields an order of magnitude speedup on the 64MB Intel
StrataFlash parts we use.

When making a copy of the block to modify, also keep a clean copy around
until we are ready to commit the block and use it to avoid unnecessary
erases.  In the non-buffer write case, also use it to avoid
unnecessary writes when the block has not been erased.  This yields a
significant speedup when doing things like zeroing a block.

Sponsored by:	DARPA, AFRL
Reviewed by:	imp (previous version)