Devices as AT45DB161 DataFlash uses non power of two page size (528)
while present alignment algorithm relies on erasesize being power
of 2.
Fix that by introducing helper functions rounding to any multiply.
Note that logic is sligthly changed to be consistent as ending
address is moved forward to include also last byte meant to be
erased while previous implementation moved it backward.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>