nios2: add early printk support

Signed-off-by: Ley Foon Tan <lftan@altera.com>

diff --cc arch/nios2/Kconfig.debug
Simple merge

diff --cc arch/nios2/include/asm/prom.h
Simple merge

diff --cc arch/nios2/kernel/Makefile
Simple merge

diff --cc arch/nios2/kernel/early_printk.c
Simple merge

diff --cc arch/nios2/kernel/prom.c
Simple merge

diff --cc arch/nios2/kernel/setup.c
Simple merge