clocksource: arm_arch_timer: Use clocksource for suspend timekeeping

The ARM architected timers keep counting during suspend so we can
mark this clocksource with the CLOCK_SOURCE_SUSPEND_NONSTOP. This
flag will indicate that this clocksource can be used for
calculating suspend time and injecting sleep time into the
timekeeping core. This will usually be more accurate than using
an external RTC or architecture specific persistent clock.

CRs-fixed: 536881
Change-Id: I882bf19a87ceb642aa069bbf26802c66c96b4426
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>