[MTD] AR7 mtd partition map

Signed-off-by: Matteo Croce <technoboy85@gmail.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Eugene Konev <ejka@imfi.kspu.ru>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>