ARM: dts: omap4: Add timer_sys_ck clocks for timers

The commit 1c7de9f2 ("clk: ti: omap4: cleanup unnecessary clock
aliases") has cleaned up all timer_sys_ck clock aliases and retained
only the timer_32k_ck clock alias. The OMAP clocksource timer driver
though still uses this clock alias when reconfiguring the parent
clock source for the timer functional clocks, so add these clocks
to all the timer nodes.

This is required by the OMAP remoteproc driver to successfully
acquire a timer and configure the source clock to be driven from
timer_sys_ck clock.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>