alpha: use .data.init_task instead of .data.init_thread.

alpha is the only architecture that uses the section name
.data.init_thread instead of .data.init_task.  So convert alpha to use
.data.init_task like everything else.

.data.init_task does not need a separate output section; this change
also moves it into the .data output section.

Signed-off-by: Tim Abbott <tabbott@mit.edu>
Cc: Richard Henderson <rth@twiddle.net>
Cc: linux-alpha@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>