[POWERPC] fix up front-LED Kconfig

This patch fixes the front-LED Kconfig issues I introduced while
creating it. Apparently having a dependency isn't enough to have the
select not evaluated or something like that.

The patch also changes the default configuration for pmac32 select the
default for the LED to be the IDE trigger. While I was at it, I
completely updated the defconfig and also added snd-aoa to it.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>