x86: Revert "Don't set up MTRRs in SPL"

This breaks Intel Edison to work. It gets laggish and unable to boot kernel.

Reverts commit 665cb18e for now
till better solution will be proposed.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Bin Meng <bmeng.cn@gmail.com>