x86: mtrr: Update MTRRs on all CPUs

When the boot CPU MTRRs are updated, perform the same update on all other
CPUs so they are kept in sync.

This avoids kernel warnings about mismatched MTRRs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>