mtd: maps: Merge physmap_of.c into physmap-core.c

There's no real reason to have two separate driver for the DT and pdata
case. Just do what we do everywhere else and handle DT and pdata
parsing in the same driver.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>