include: add includes includes to make fdt.h, of.h and state.h self contained ...

Otherwise compilation may fail with:

include/fdt.h:11:15: error: unknown type name 'uint64_t'
 static inline uint64_t fdt64_to_cpu(uint64_t x)

include/of.h:22:19: error: field 'list' has incomplete type
  struct list_head list;

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

state: add framework for persistent state handling ...

This patch adds a framework to describe, access, store and restore a set of
variables. A state variable set can be fully described in a devicetree node.
This node could be part of the regular devicetree blob or it could be an extra
devicetree solely for the state. The state variable set contains variables of
different types and a place to store the variable set.

For more information see:
    Documentation/devicetree/bindings/barebox/barebox,state.rst

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>