bindings: arm: msm: Added documentation for ipc spinlock

Interprocessor Communication Spinlock

--Dedicated Hardware Implementation--

Required properties:

- compatible : should be "qcom,ipc-spinlock-sfpb"

- reg : the location and size of the spinlock hardware

- qcom,num-locks : the number of locks supported

Example:

	qcom,ipc-spinlock@fd484000 {

		compatible = "qcom,ipc-spinlock-sfpb";

		reg = <0xfd484000 0x1000>;

		qcom,num-locks = <32>;

	};

--LDREX Implementation--

Required properties:

- compatible : should be "qcom,ipc-spinlock-ldrex"

- reg : the location and size of the shared lock memory

Example:

	qcom,ipc-spinlock@fa00000 {

		compatible = "qcom,ipc-spinlock-ldrex";

		reg = <0xfa00000 0x200000>;

	};