Add NPU device type to capabilities

In preparation to support the Linux kernel driver directly managing the
NPU without a subsystem. A NPU device type has been added to the
capabilities to be able to specify what kind of NPU is used.

Change-Id: I45345b7d75d234f821d70b858453d3af2a99194e
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>