dt-bindings: counter: new bindings for TI eQEP

This documents device tree binding for the Texas Instruments Enhanced
Quadrature Encoder Pulse (eQEP) Module found in various TI SoCs.

Signed-off-by: David Lechner <david@lechnology.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>