'struct pmic_table' is not modified in these drivers.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
   3811	    786	      0	   4597	   11f5	drivers/acpi/pmic/intel_pmic_xpower.o

   text	   data	    bss	    dec	    hex	filename
   4147	    450	      0	   4597	   11f5	drivers/acpi/pmic/intel_pmic_xpower.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/a6c9b1bcdf259adabbcaf91183d3f5ab87a98600.1719644292.git.christophe.jaillet@wanadoo.frReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>