rng: tighten up domain <controller> schema

rng: tighten up domain <controller> schema

The rng schema for <controller> had been non-specific about which
types of controllers allowed which models, and also allowed the
num_queues attribute (since that hasn't been released yet, should we
rename it to "numQueues"?) and <master> subelement to be included for
any controller type. In reality, half of the models are allowed only
for type='scsi', and the other half only for type='usb', num_queues is
allowed only for type='scsi', and <master> only for type='usb'.

This patch makes a separate <group> for type='scsi' and type='usb',
with each group allowing only the appropriate model values, and
allowing num_queue and <master> only when appropriate.

<interleave> also hadn't been specified, forcing a specific order of
subelements, which should never be done. (Note that the <interleave>
had to surround the main element attributes that are in the <group>
subelements, due to one of the <group>s containing a subelement).