drivers: make driver names consistent

drivers: make driver names consistent

As discussed in the past release, driver names are modified
to be more consistent, and the future driver should follow
this new convention.

Driver names consist of:
"driver category"_"driver folder name"_"optional extra name".

For example:
- Crypto null driver       -> "crypto_null"
- Network IXGBE VF driver  -> "net_ixgbe_vf"

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>