[ioapi] Centralise notion of PAGE_SIZE

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/include/ipxe/x86_io.h

  *
  */
 
+/** Page shift */
+#define PAGE_SHIFT 12
+
 /*
  * Physical<->Bus and Bus<->I/O address mappings
  *

src/include/ipxe/io.h

 #include <config/ioapi.h>
 #include <ipxe/uaccess.h>
 
+/** Page size */
+#define PAGE_SIZE ( 1 << PAGE_SHIFT )
+
+/** Page mask */
+#define PAGE_MASK ( PAGE_SIZE - 1 )
+
 /**
  * Calculate static inline I/O API function name
  *

src/include/ipxe/virtio-ring.h

 #ifndef _VIRTIO_RING_H_
 # define _VIRTIO_RING_H_
-#define PAGE_SHIFT (12)
-#define PAGE_SIZE  (1<<PAGE_SHIFT)
-#define PAGE_MASK  (PAGE_SIZE-1)
 
 /* Status byte for guest to report progress, and synchronize features. */
 /* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */