drm/xe: Define Virtual Function Identifier

According to the PCI Express specification, the SR-IOV Virtual
Functions (VFs) are numbered starting with 1 (VF1, VF2, ...).
Additionally, both driver and GuC will refer to Physical Function
(PF) as VF0. Define helper macro to represent VFn and PF.
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20240104222031.277-3-michal.wajdeczko@intel.comSigned-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>

drivers/gpu/drm/xe/xe_sriov_types.h

@@ -8,6 +8,18 @@
 
 #include <linux/build_bug.h>
 
+/**
+ * VFID - Virtual Function Identifier
+ * @n: VF number
+ *
+ * Helper macro to represent Virtual Function (VF) Identifier.
+ * VFID(0) is used as alias to the PFID that represents Physical Function.
+ *
+ * Note: According to PCI spec, SR-IOV VF's numbers are 1-based (VF1, VF2, ...).
+ */
+#define VFID(n)		(n)
+#define PFID		VFID(0)
+
 /**
  * enum xe_sriov_mode - SR-IOV mode
  * @XE_SRIOV_MODE_NONE: bare-metal mode (non-virtualized)