pinctrl: single: make two arrays static const, reduces object code size

Don't populate the read-only arrays prop2 and prop4 on the stack, instead
make them static const.  Makes the object code smaller by over 230 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  28235	   5820	    192	  34247	   85c7	drivers/pinctrl/pinctrl-single.o

After:
   text	   data	    bss	    dec	    hex	filename
  27839	   5980	    192	  34011	   84db	drivers/pinctrl/pinctrl-single.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>