documentation: Add document for memory dump

Qualcomm Technologies Inc. memory dump driver

QTI memory dump driver allows various client subsystems to register and

allocate respective dump regions. At the time of deadlocks or cpu hangs

these dump regions are captured to give a snapshot of the system at the

time of the crash.

Required properties:

-compatible: "qcom,mem-dump"

-memory-region: phandle to the CMA region. The size of the CMA region

		should be greater than sum of size of all child nodes

		to account for padding.

If any child nodes exist the following property are required:

-qcom,dump-size: The size of memory that needs to be allocated for the

		 particular node.

-qcom,dump-id: The ID within the data dump table where this entry needs

	       to be added.

Example:

	mem_dump {

		compatible = "qcom,mem-dump";

		memory-region = <&dump_mem>;

		rpmh_dump {

			qcom,dump-size = <0x2000000>;

			qcom,dump-id = <0xEC>;

		};

	};