x86: Remove cpu_init_r() for x86

Since cpu_init_interrupts() was moved out of cpu_init_r(), it is
useless to keep cpu_init_r() for x86, thus remove it.

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