i965: Remove unused devinfo revision

i965: Remove unused devinfo revision

I left the function to obtain the revision because it is, and will continue to
be useful in the future. I'd rather not have to dig it up every time we need it.
Comments left at the implementation to say as much.

This was accidentally left here when I moved the early platform support:
commit 28ed1e08e8ba98ebd4ff0b56326372f0df9c73ad
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Fri Aug 7 13:58:37 2015 -0700

    i965/skl: Remove early platform support

Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>