dt-bindings: net: bluetooth: qualcomm: describe regulators for QCA6390

QCA6390 has a compatible listed in the bindings but is missing the
regulators description. Add the missing supply property and list the
required ones in the allOf section.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>