arch/alpha: remove depends on CONFIG_EXPERIMENTAL

The CONFIG_EXPERIMENTAL config item has not carried much meaning for a
while now and is almost always enabled by default. As agreed during the
Linux kernel summit, remove it from any "depends on" lines in Kconfigs.

CC: Richard Henderson <rth@twiddle.net>
CC: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Anna-Maria Gleixner <anna-maria@glx-um.de>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Matt Turner <mattst88@gmail.com>