x86: Add another set of MSR accessor functions

commit 22085a66c2fab6cf9b9393c056a3600a6b4735de upstream.

We very often need to set or clear a bit in an MSR as a result of doing
some sort of a hardware configuration. Add generic versions of that
repeated functionality in order to save us a bunch of duplicated code in
the early CPU vendor detection/config code.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1394384725-10796-2-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
[bwh: Backported to 3.2: s/wrmsrl_safe/checking_wrmsrl/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>