msm: timer: Fix SMP build error

Fix build breakage on SMP=y builds due to 0f7b332f (ARM:
consolidate SMP cross call implementation, 2011-04-03)

arch/arm/mach-msm/timer.c: In function 'local_timer_setup':
arch/arm/mach-msm/timer.c:295: error: implicit declaration of
function 'gic_enable_ppi'

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>