platform/x86/intel/ifs: IFS cleanup

Cleanup incorporating misc review comments

 - Remove the subdirectory intel_ifs/0 for devicenode [1]
 - Make plat_ifs_groups non static and use it directly without using a
    function [2]

Link: https://lore.kernel.org/lkml/Y+4kQOtrHt5pdsSO@kroah.com/ [1]
Link: https://lore.kernel.org/lkml/Y9nyxNesVHCUXAcH@kroah.com/

  [2]

Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230322003359.213046-4-jithu.joseph@intel.com


Signed-off-by: Hans de Goede <hdegoede@redhat.com>