Remove nested 'ipmi' dict from driver_info

driver_info do not support nested objects. Self-namespace will be used
to distinguish parameters from one driver to another.

Change-Id: Ia720fac4b60aa0aa18406e0ba61d8a0a8c5c8a78
Partial-Bug: #1236533
Merge "Remove nested 'ipmi' dict from driver_info"