Add buffer alignment and max size to NPU driver

The direct drive and subsystem NPU setups, have different restrictions
for buffer alignment and max size. To accommodate this, the device
instance now have a buffer configuration that will be used when creating
buffers.

Change-Id: I0a258b70cf77eacd4d8dc7d9322dea393ed02dbd
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>