This reverts commit 904464b9.

The problem pointed out by commit 904464b9 ("ARM: 7655/1:
smp_twd: make twd_local_timer_of_register() no-op for nosmp")
doesn't exist anymore.

We can safely boot with nosmp and the warning won't show up.

The other side benefit of this patch is that TWD has a chance
to probe on single-core A9 systems such as AM437x which sport
TWD.

While at that, also drop SMP dependency from TWD's Kconfig entry.

Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>