x86: cpu: Skip init code when chain loading

x86: cpu: Skip init code when chain loading

When U-Boot is not the first-stage bootloader the interrupt and cache init
must be skipped, as well as init for various peripherals. Update the code
to add checks for this.

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