tile: support CONTEXT_TRACKING and thus NOHZ_FULL

Add the TIF_NOHZ flag appropriately.

Add call to user_exit() on entry to do_work_pending() and on entry
to syscalls via do_syscall_trace_enter(), and also the top of
do_syscall_trace_exit() just because it's done in x86.

Add call to user_enter() at the bottom of do_work_pending() once we
have no more work to do before returning to userspace.

Wrap all the trap code in exception_enter() / exception_exit().

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

diff --cc arch/tile/Kconfig
Simple merge

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

diff --cc arch/tile/kernel/process.c
Simple merge

diff --cc arch/tile/kernel/ptrace.c
Simple merge

diff --cc arch/tile/kernel/single_step.c
Simple merge

diff --cc arch/tile/kernel/traps.c
Simple merge

diff --cc arch/tile/kernel/unaligned.c
Simple merge

diff --cc arch/tile/mm/fault.c
Simple merge