Prepare making PAT and MTRR support independent from each other by
moving some code needed by both out of the MTRR-specific sources.

  [ bp: Massage commit message. ]
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221102074713.21493-7-jgross@suse.comSigned-off-by: Borislav Petkov <bp@suse.de>