platform/x86/intel/vsec: Decouple add/link helpers from PCI

platform/x86/intel/vsec: Decouple add/link helpers from PCI

This refactor prepares for adding ACPI-enumerated PMT endpoints. While
intel_vsec is bound to PCI today, some helpers are used by code that will
also register PMT endpoints from non-PCI (ACPI) paths. Clean up
PCI-specific plumbing where it isn’t strictly required and rely on generic
struct device where possible.

Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Link: https://patch.msgid.link/20260313015202.3660072-4-david.e.box@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>