cris: update comments for generic idle conversion

As of commit 8dc7c5ec

 ("cris: Use generic idle loop"), cris no
longer provides cpu_idle().

- On cris-v10, etrax_gpio_wake_up_check() is called from default_idle()
  instead of cpu_idle(),

- On cris-v32, etrax_gpio_wake_up_check() is not called from
  default_idle(), so remove this (copy-and-paste?) part.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>