pinctrl: ocelot: Constify some structures

pinctrl: ocelot: Constify some structures

'struct ocelot_match_data and 'struct irq_chip' are not modified in this
driver.

Constifying these structures moves some data to a read-only section, so
increase overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  41459	   9008	     80	  50547	   c573	drivers/pinctrl/pinctrl-ocelot.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  42803	   7640	     80	  50523	   c55b	drivers/pinctrl/pinctrl-ocelot.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/32edcf0567fffd0b1a219e7e2dad7e0bd8c5aaf4.1734023550.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>