Add the write verification buffer to the dataflash.  The mtd_dataflash has
the CONFIG_DATAFLASH_WRITE_VERIFY so is better a change to Kconfig.
Signed-off-by: NMichael Trimarchi <trimarchimichael@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>