Bluetooth: btusb: Update firmware filename for Intel 9x60 and later

The format of Intel Bluetooth firmware for bootloader product is
ibt-<hw_variant>-<device_revision_id>.sfi and .ddc.

But for the SKU's 9x60, there a 3 variants of FW, which cannot be
differentiated just with hw_variant and devision_revision_id.
So to pick the appropriate FW file for 9x60 SKU's, it will be
differentiated using hw_variant, hw_revision and fw_revision rather
than hw_variant and device_revision_id only.

Format will be like this:
ibt-<hw_variant>-<hw_revision>-<fw_revision>.sfi and .ddc

Signed-off-by: Jaya P G <jaya.p.g@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>