power: supply: wm831x: Constify struct chg_map and some arrays

'struct chg_map' is not modified in this driver.

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

While at it, also constify a few other arrays.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  14263	   1744	      0	  16007	   3e87	drivers/power/supply/wm831x_power.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  14695	   1288	      0	  15983	   3e6f	drivers/power/supply/wm831x_power.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/0edde57b691db7f920d121fdbd5ebc3fb24f30f1.1743787625.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>