ARM: dts: OMAP5: Remove clock-frequency field for cpu timers

The arm arch timers frequency are now programmed in the CNTFREQ
per-cpu register by the timer code using the secure API [1].
So remove the redundant entry from the dts.

[1] http://marc.info/?l=linux-omap&m=138139106312786&w=2

Signed-off-by: Sricharan R <r.sricharan@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>