iwlwifi: move debug options into submenu

more debug options being added so it is useful to move them
into a submenu for ease of readability when using config commands
like make menuconfig and make xconfig

Signed-off-by: Jay Sternberg <jay.e.sternberg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>