dt: Add of_device_compatible_match()

This provides an equivalent of of_fdt_match() for non-flat trees.

This is more practical than matching an array of of_device_id structs
when converting a bunch of existing users of of_fdt_match().

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>