Adds xiv_chap to xiv/ds8k driver configuration

In order to support CHAP, xiv_chap was added to
the driver configuration. Valid values are disabled
and enabled (default: disabled)

Change-Id: I0c68f581ad78a87a506b00ab308806f4a8fa78a8
DocImpact
Closes-Bug: #1288816
Merge "Adds xiv_chap to xiv/ds8k driver configuration"