inquiry: add nominal-form-factor enum and block devchar pretty print

Add an enum to map the NominalFormFactor strings to values.
Add pretty print for the BlockDeviceCharacteristics VPD page to the
inquiry.py utility.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Merge pull request #36 from sahlberg/inquiry-more-updates

inquiry: add nominal-form-factor enum and block devchar pretty print