SystemACE: Remove

This driver is no longer used on any supported platform in U-Boot and
there is no interest in maintaining it further from people that have
used it historically.

Cc: Simon Glass <sjg@chromium.org>
Cc: Michal Simek <michal.simek@xilinx.com>
c: Alexey Brodkin <alexey.brodkin@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>