Add a new tool to convert FreeBSD USB device IDs to the format we use

Add a new tool to convert FreeBSD USB device IDs to the format we use
in DragonFly.  This eases the process of getting new IDs from FreeBSD, which
is currently necessary due to the fact that their lists are much longer
than our lists :)

To use the tool you need the usbdevs file from FreeBSD:
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/dev/usb/usbdevs

usage: ./convert_usb_ids.sh [-d] < FREEBSD-IDs > DFLY-IDs

The tool operates in two modi.  The first one is for umass entries and
converts entries like this

  { USB_VENDOR_ADDONICS2, USB_PRODUCT_ADDONICS2_CABLE_205, RID_WILDCARD,
	  UMASS_PROTO_SCSI | UMASS_PROTO_BBB,
	  NO_QUIRKS
  },

to

  /* Addonics Cable 205  */
  { .vendor = 0x0bf6, .product = 0xa001, release = WILDCARD_ID,
    .proto  = UMASS_PROTO_SCSI | UMASS_PROTO_BBB,
    .quirks = NO_QUIRKS
  },

Pass -d option to use umass modi.  The second one converts easier
entries:

  {{ USB_VENDOR_ACEECA, USB_PRODUCT_ACEECA_MEZ1000 }, PALM4 },

to

  {{ USB_DEVICE(0x4766, 0x0001) }, PALM4 }, /* Aceeca MEZ1000 RDA  */

NOTE:  Due to some peculiarities of the usbdevs file, it is possible that you
can get duplicate entries or wrong comments.  So make sure that your converted
entry is correct.