nvdimm: constify device_type structures

Declare device_type structure as const as it is only stored in the
type field of a device structure. This field is of type const, so add
const to declaration of device_type structure.

File size before:
  text	   data	    bss	    dec	    hex	filename
  19278	   3199	     16	  22493	   57dd	nvdimm/namespace_devs.o

File size after:
  text	   data	    bss	    dec	    hex	filename
  19929	   3160	     16	  23105	   5a41	nvdimm/namespace_devs.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

path: root/tools/perf/pmu-events/arch/x86/skylake/other.json

[
    {
        "PublicDescription": "This event counts the number of hardware interruptions received by the processor.",
        "EventCode": "0xCB",
        "Counter": "0,1,2,3",
        "UMask": "0x1",
        "EventName": "HW_INTERRUPTS.RECEIVED",
        "SampleAfterValue": "100003",
        "BriefDescription": "Number of hardware interrupts received by the processor.",
        "CounterHTOff": "0,1,2,3,4,5,6,7"
    }
]