acpi, nfit: constify *_attribute_group

File size before:
   text	   data	    bss	    dec	    hex	filename
  20792	   1580	    994	  23366	   5b46	drivers/acpi/nfit/core.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  20968	   1388	    994	  23350	   5b36	drivers/acpi/nfit/core.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>