clocksource: exynos_mct: Set IRQ affinity when the CPU goes online

Some variants of Exynos MCT, namely exynos4210-mct at the moment, use
normal, shared interrupts for local timers. This means that each
interrupt must have correct affinity set to fire only on CPU
corresponding to given local timer.

However after recent conversion of clocksource drivers to not use the
local timer API for local timer initialization any more, the point of
time when local timers get initialized changed and irq_set_affinity()
fails because the CPU is not marked as online yet.

This patch fixes this by moving the call to irq_set_affinity() to
CPU_ONLINE notification, so the affinity is being set when the CPU goes
online.

This fixes a regression introduced by commit
	ee98d27d ARM: EXYNOS4: Divorce mct from local timer API
which rendered all Exynos4210 based boards unbootable due to
failing irq_set_affinity() making local timers inoperatible.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>