EDAC/igen6: Constify struct res_config

The res_config structs 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, as an example:

  Before:
  ======
     text	   data	    bss	    dec	    hex	filename
    36777	   2479	   4304	  43560	   aa28	drivers/edac/igen6_edac.o

  After:
  =====
     text	   data	    bss	    dec	    hex	filename
    37297	   1959	   4304	  43560	   aa28	drivers/edac/igen6_edac.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Link: https://lore.kernel.org/r/a06153870951a64b438e76adf97d440e02c1a1fc.1738355198.git.christophe.jaillet@wanadoo.fr