x86: baytrail: Issue full system reset in reset_cpu()

x86: baytrail: Issue full system reset in reset_cpu()

With MRC cache enabled, when typing 'reset' in the U-Boot shell,
BayTrail FSP initialization hangs at "Configuring Memory Start":

  Setting BootMode to 0
  Install PPI: 1F4C6F90-B06B-48D8-A201-BAE5F1CD7D56
  Register PPI Notify: F894643D-C449-42D1-8EA8-85BDD8C65BDE
  About to call MrcInit();
  BayleyBay Platform Type
  CurrentMrcData.BootMode = 4
  Taking Fastboot path!
  Configuring Memory Start...

Changing reset_cpu() to do a full system reset fixes this issue.

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