Inquiry: page_length/page_code is common for all evpd==1 pages

Break out the unmarshalling of page_length and page_code from
SUPPORTED_VPD_PAGES since these two fields will be common for all
vpd pages when evpd==1

At the same time, change the unmarshalling of the two byte length field
to use the scsi_ba_to16 helper instead of manually unmarshalling it.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Inquiry: add support for BlockLimits VPD page

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Merge pull request #14 from sahlberg/blocklimits

Blocklimits