ARM: Default to using optimized memset and memcpy routines

We have long had available optimized versions of the memset and memcpy
functions that are borrowed from the Linux kernel.  We should use these
in normal conditions as the speed wins in many workflows outweigh the
relatively minor size increase.  However, we have a number of places
where we're simply too close to size limits in SPL and must be able to
make the size vs performance trade-off in those cases.

Cc: Philippe Reynes <tremyfr@yahoo.fr>
Cc: Eric Jarrige <eric.jarrige@armadeus.org>
Cc: Heiko Schocher <hs@denx.de>
Cc: Magnus Lilja <lilja.magnus@gmail.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Chander Kashyap <k.chander@samsung.com>
Cc: Akshay Saraswat <akshay.s@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>