ARC: remove extraneous __KERNEL__ guards

Verified by doing make headers_install as none of these files are
exported to userspace

diff --cc arch/arc/include/asm/arcregs.h
Simple merge

diff --cc arch/arc/include/asm/atomic.h
Simple merge

diff --cc arch/arc/include/asm/bitops.h
Simple merge

diff --cc arch/arc/include/asm/current.h
Simple merge

diff --cc arch/arc/include/asm/irqflags.h
Simple merge

diff --cc arch/arc/include/asm/processor.h
Simple merge

diff --cc arch/arc/include/asm/string.h
Simple merge

diff --cc arch/arc/include/asm/syscalls.h
Simple merge

diff --cc arch/arc/include/asm/thread_info.h
Simple merge