platform/x86/intel/vsec: Enhance and Export intel_vsec_add_aux()

Remove static for intel_vsec_add_aux() and export this interface so that
it can be used by other vsec related modules.

This driver creates aux devices by parsing PCI-VSEC, which allows
individual drivers to load on those devices. Those driver may further
create more devices on aux bus by parsing the PCI MMIO region.

For example, TPMI (Topology Aware Register and PM Capsule Interface)
creates device nodes for power management features by parsing MMIO region.

When TPMI driver creates devices, it can reuse existing function
intel_vsec_add_aux() to create aux devices with TPMI device as the parent.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20230202010738.2186174-3-srinivas.pandruvada@linux.intel.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>