clocksource/drivers/spreadtrum: Add timer driver for the Spreadtrum SC9860 platform

The Spreadtrum SC9860 platform will use the architected timers as local
clock events, but we also need a broadcast timer device to wake up the
CPUs when the CPUs are in sleep mode.

The Spreadtrum timer can support 32-bit or 64-bit counters, as well as
supporting period mode or one-shot mode.

Signed-off-by: Baolin Wang <baolin.wang@spreadtrum.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1515418139-23276-8-git-send-email-daniel.lezcano@linaro.org


[ Minor readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>