nios2: Signal handling support

This patch adds support for signal handling.

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

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

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

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

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

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