fdt: implement dev_get_addr_name()

fdt: implement dev_get_addr_name()

This function parses the reg property based on an index found in the
reg-names property. This is required for bindings that are written
using reg-names rather than hard-coding indices in reg.

Signed-off-by: Stephen Warren <[email protected]>
Acked-by: Simon Glass <[email protected]>