msm: timer: Use GPT for clockevents and DGT for clocksource

The clocksource shouldn't stop ticking when the clockevent stops.
This is exactly what happens today with MSM timers. The same
hardware is used for both the clockevent and the clocksource
because the ratings of the two are the same.

Fix this by registering a clockevent based on the GPT and a
clocksource based on the DGT. This removes any other possible
configuration (e.g. a GPT clocksource and a DGT clockevent) but
that shouldn't be a big issue since we want higher precision
timing than high precision scheduling interrupts.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: David Brown <davidb@codeaurora.org>