Use ccm device

[palainp]

This is a WIP and the following pins are needed so far:

• opam pin git+https://github.com/palainp/chamelon.git#kv-500 -y
• opam pin git+https://github.com/mirage/mirage.git#add-ccm-block -y

The first one include some dumb implementation of the missing function in mirage-kv-5.0.0, the second one adds ccm_block in mirage.

This should hopefully respond to #11 :)