arch/arm/Makefile: Enable pipe compiling

-pipe

Use pipes rather than temporary files for communication between the various stages of
compilation. This fails to work on some systems where the assembler is unable to read
from a pipe; but the GNU assembler has no trouble.
Apply BFQ 3.4.0-v6r2:

http://algo.ing.unimo.it/people/paolo/disk_sched/sources.php

Signed-off-by: Paul Beeler <sparksco@gmail.com>