mtd: physmap_of: Add multiple regions and concatenation support

This patch adds support to handle multiple non-identical chips in one
flash device tree node. It also adds concat support to physmap_of. This
makes it possible to support e.g. the Intel P30 48F4400 chips which
internally consists of 2 non-identical NOR chips on one die. Additionally
partitions now can span over multiple chips.

To describe such a chip's, multiple "reg" tuples are now supported in one
flash device tree node. Here an dts example:

        flash@f0000000,0 {
                #address-cells = <1>;
                #size-cells = <1>;
                compatible = "cfi-flash";
                reg = <0 0x00000000 0x02000000
                       0 0x02000000 0x02000000>;
                bank-width = <2>;
                partition@0 {
                        label = "test-part1";
                        reg = <0 0x04000000>;
                };
        };

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>