mtd: sh_flctl: Add device tree support

The flctl can now be probed via device tree setup in addition to the
existing platform data way.

SoC specific setup data is set in the .data member of the OF match, so
kept within the driver itself, while board/user specific setup - like
partitioning - is taken from the device tree.

Actual configuration is added for the SoC sh7372.

Signed-off-by: Bastian Hecht <hechtb@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>