Tegra Virtual Storage driver for OOPS partition

Virtual Storage Driver is the front end driver that interfaces with
-  the Storage Virtualization System for Tegra SOC OOPS partition and
-  the pstore system for storing OOPS/panic logs

Required Properties:
- compatible: should be "nvidia,tegra-hv-oops-storage"
- instance:   to identify a specific instance of the device
- ivc:        ivc channel to used for communication with Virtualization System
- mempool:    mempool used for data transfers with Virtualization System
- pstore_max_reason: one of KMSG_DUMP_* values from kmsg_dump.h. Driver only
	supports KMSG_DUMP_OOPS (value = 2) which allows PANIC and OOPS logs
	to be stored.  KMSG logs above this reason level will be ignored.
- pstore_kmsg_size: record size (should be block size aligned) for KMSG logs.
	Default is 64KB.

Example:
	tegra_virt_storage31 {
		compatible = "nvidia,tegra-hv-oops-storage";
		status = "okay";
		pstore_max_reason = <2>;
		pstore_kmsg_size = <0x10000>;
		instance = <31>;
		ivc = <&tegra_hv 230>;
		mempool = <69>;
	};
