x86/resctrl: Add __init attribute to rdt_get_mon_l3_config()

In an upcoming change, rdt_get_mon_l3_config() needs to call rdt_cpu_has() to
query the monitor related features. It cannot be called right now because
rdt_cpu_has() has the __init attribute but rdt_get_mon_l3_config() doesn't.

Add the __init attribute to rdt_get_mon_l3_config() that is only called by
get_rdt_mon_resources() that already has the __init attribute. Also make
rdt_cpu_has() available to by rdt_get_mon_l3_config() via the internal header
file.

Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/20230113152039.770054-8-babu.moger@amd.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>