arm: zynq: Use standard timer binding

arm: zynq: Use standard timer binding

Use cdns,ttc because this driver is Cadence Rev06
Triple Timer Counter and everybody can use it
without xilinx specific function name or probing.

Also use standard dt description for timer
and also prepare for moving to clocksource
initialization.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>