platform: fpga/common: Add a fdt parsing helper functions

Different DT based platforms from the sam family may reuse IP blocks with
different configurations. These different configurations can be obtained
by parsing the device tree.

Add a FDT parser framework that can parse various device configurations from
device tree. Currently, the parsing algorithms doesn't cover all the use cases
or possible combination of DT configurations. It will be improved over time.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>