Refactor NPU buffers to share backing memory

For direct drive, buffers must be placed at the expected offsets when
they are allocated. To be able to support this, buffers are now
allocated in batches and they share the same backing memory.

This has changed the UAPI in a way that is not backward compatible and
thus the major version has been bumped. Due to the buffer offset
requirement, buffers no longer support being memory mapped and instead
the data needs to be accessed using the read/write calls.

Driver library and tests have been updated accordingly to the new
changes.

Change-Id: I9ba8be5f95a2c231e32e9c2eb6dd690b95dd506e
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>