uboot-imx

sandbox: Add improved RAM simulation

Using mmap to allocate memory from the OS for RAM simulation we can use
u-boot own malloc implementation.

Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Matthias Weisser <weisserm@arcor.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>