Powerpc powernv platforms allow access to certain system flash devices
through a firmwarwe interface. This change adds an mtd driver for these
flash devices.

Minor updates from Jeremy Kerr and Joel Stanley.
Signed-off-by: NCyril Bur <cyrilbur@gmail.com>
Signed-off-by: NJoel Stanley <joel@jms.id.au>
Signed-off-by: NJeremy Kerr <jk@ozlabs.org>
Reviewed-by: NNeelesh Gupta <neelegup@linux.vnet.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>