Move NPU functions and structs to common NPU file

NPU specific functions and structs should be kept in the NPU related
files to keep the direct device decoupled from the NPUs as much as
possible

Change-Id: I440e46b6c0e46f43e1afe635464eff0bcfa28c18
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>