JFFS2-on-DataFlash support

[Andrew Victor]

hi,

This patch adds support for JFFS2-on-DataFlash devices.
DataFlash is NOR flash, with a NAND-like layout, but doesn't include
NAND features like OOB areas.

So for Dataflash, can_mark_obsolete = false and the NAND write buffering
code (wbuf.c) is used.

Since the DataFlash chip will automatically erase pages when writing,
the cleanmarkers are not needed - so cleanmarker_oob = false and
cleanmarker_size = 0

DataFlash page-sizes are not a power of two (they're multiples of 528
bytes).  There are a few places in JFFS2 code where sector_size is used
as a bitmask.  A new macro (SECTOR_ADDR) was defined to calculate these
sector addresses. If CONFIG_JFFS2_FS_DATAFLASH is not selected, the
original (faster) bitmask operation will still be used.

Also in scan.c, the EMPTY_SCAN_SIZE was a constant of 1024. 
Since this could be larger than the sector size of the DataFlash, this
is now basically set to MIN(sector_size, 1024).

(Patch is against the latest version in CVS)


Regards,
  Andrew Victor

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