kdb: add rdmsr and wrmsr commands for i386

[bernie at codewiz.org (Bernardo Innocenti)]

Jordan Crouse wrote:

> Can you break this up with a : between the high dword and the low dword?
> That makes it easier to parse when debugging.

Good idea, but I used "_" instead because it's what AMD uses in their
documentation and it looks better with a "0x" prefix.

> Also, would it make sense to coordinate the order of the high and low
> dwords with the order they are specified with 'wrmsr'?  

Yeah, I did it as suggested by Mitch.  Here's a thrid
revision of the patch with everything included: