x86: remove unused function amd_init_cpu()

There are no users for the function amd_init_cpu() defined in
arch/x86/kernel/cpu/amd.c. This patch removes this routine.

This patch was build-tested using defconfigs for i386 and x86_64,
and a few randconfig instances. Runtime tests were performed by
booting 32- and 64-bit x86 boxen up to the shell prompt.

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>