MSR support design choice

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

     A while ago, I posted preliminary code for MSR support, but
didn't get any feedback.  There is a design choice that I would
really like to get feedback on.  This is the question of whether
to make userland switch CPUs if it wants to execute the MSR on a
particular CPU or have the kernel do it.  If the former, there is
no need to put the CPU number in the structure that gets passed
during the ioctl().  Also, it's much easier to have userland do
the switching.  Having the kernel do it would require a xcall.