msm: timer: Remove SoC specific #ifdefs

The timer frequency is currently ifdefed in addition to setting
the DGT clock's divider value on SCORPIONMP targets. Setup the
frequency dynamically using the existing cpu_is_*() branches and
assign a custom clocksource read function for 7x01a to get the
shift out of the generic path.

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>