dt-bindings: net: broadcom-bluetooth: Add BCM20702A1 compatible string

The BCM20702A1 is a Bluetooth 4.0 chip from Broadcom. It is found in the
Ampak AP6210 WiFi+BT module, identified from the read verbose config info
command response. However the Bluetooth firmware provided by vendors uses
the name BCM20710. This patch elects to use the chip ID returned by the
chip for the compatible string.

Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>