nvme-cli: Western Digital/HGST plug-in.

nvme-cli: Western Digital/HGST plug-in.

This patch adds support for Vendor unique commands for
Western Digital/HGST devices. Following commands are
supported in current version of this extension:-

1.cap-diag        WDC Capture-Diagnostics
2.drive-log       WDC Drive Log
3.get-crash-dump  WDC Crash Dump
4.id-ctrl         WDC identify controller
5.purge           WDC Purge
6.purge-monitor   WDC Purge Monitor
7.smart-log-add   WDC Additional Smart Log

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@hgst.com>