lib/types: Create common file for type definitions

The device and boot_option types are defined in pb-protocol.h, but
aren't really specific to the procotol. This means a lot of
non-messaging-related files are #including the protocol definitions
unnecessarily.

This change separates the types out into lib/types/types.h.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Geoff Levand <geoff@infradead.org>