Check for VID bits consistency

[khali]

Sometimes monitoring chips have fewer VID inputs than the CPU would need. In that case it's pretty clear that the VID reading can't be reported properly so it should be disabled by the driver. See for example:
 http://lists.lm-sensors.org/pipermail/lm-sensors/2011-June/032957.html

[khali]

One possible way to implement this check would be to add a parameter to function vid_which_vrm:

u8 vid_which_vrm(int nbits)

This parameter would let the caller optionally specify how many VID inputs it supports. vid_which_vrm would then only return a VRM code if the VRM standard doesn't need more bits. Otherwise it would return 0, effectively disabling the VID support.