Use BuxtonArray for deserialization

Instead of passing around a pointer to BuxtonDatas(*), and a
length parameter, we now use the opaque BuxtonData structure,
which enables us to know the exact length of the array as
well as access the content with ease.

This is designed to match the changes made to the message
serialization code.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>