Put all the debugging output behind "mtrr=debug" and get rid of
"mtrr_cleanup_debug" which wasn't even documented anywhere.

No functional changes.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230531174857.GDZHeIib57h5lT5Vh1@fat_crate.local