dt-bindings: bluetooth: Utilize PMU abstraction for WCN6750

We are now using the on-chip PMU node for power sequencing to manage the
enable/disable functionality of Bluetooth. Consequently, the inputs
previously marked as required under the Bluetooth node can be removed.

For instance, the enable GPIO is now managed by the PMU node with the
property bt-enable-gpios.

Signed-off-by: Janaki Ramaiah Thota <quic_janathot@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>