Add device capabilities caching in kernel driver

To not have to fetch the capabilities from the device for each time they
are requested with the UAPI, the kernel driver will now fetch and save
the capabilities during the device initialization and use the saved copy
for the UAPI requests.

With this change, the character device creation in the device
initialization has been moved to be the last step so the capabilities
are fetched and saved before the character device is created.

Change-Id: I57956aedb983fbc1765d45906a1c6182e2cd5b96