x86: broadwell: Add support for SDRAM setup

x86: broadwell: Add support for SDRAM setup

Broadwell uses a binary blob called the memory reference code (MRC) to start
up its SDRAM. This is similar to ivybridge so we can mostly use common code
for running this blob.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Bin Meng <bmeng.cn@gmail.com>