x86/mtrr: Make message for disabled MTRRs more descriptive

Instead of just saying "Disabled" when MTRRs are disabled for any
reason, tell what is disabled and why.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20221205080433.16643-3-jgross@suse.com