x86/resctrl: Add printf attribute to log function

Mark the function with the __printf attribute to allow the compiler to
more thoroughly typecheck its arguments against a format string with
-Wformat and similar flags.

 [ bp: Massage commit message. ]

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lkml.kernel.org/r/20201221160009.3752017-1-trix@redhat.com