x86/mtrr: Split MTRR-specific handling from cache dis/enabling

Split the MTRR-specific actions from cache_disable() and cache_enable()
into new functions mtrr_disable() and mtrr_enable().

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221102074713.21493-6-jgross@suse.com


Signed-off-by: Borislav Petkov <bp@suse.de>