uboot-phytec

dtoc: Move BytesToValue() and GetEmpty() into PropBase

These functions are currently in a separate fdt_util file. Since they are
only used from PropBase and subclasses, it makes sense for them to be in the
PropBase class.

Move these functions into fdt.py along with the list of types.

Signed-off-by: Simon Glass <sjg@chromium.org>