nios2: Miscellaneous header files

This patch introduces a few nios2-specific header files.

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

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

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

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

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

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