[MTD] partitioning utility predicates

Move mtd_has_partitions() and mtd_has_cmdlinepart() inlines from a
DaVinci-specific driver to the <linux/mtd/partitions.h> header.

Use those to eliminate #ifdefs in two drivers which had their own
definitions of mtd_has_partitions().

Quite a lot of other MTD drivers could benefit from using use one or both
of these to remove #ifdeffery.  Maybe some Janitors would like to help.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>