clocksource/drivers/cadence-ttc: Use ttc driver as platform driver

Currently TTC driver is TIMER_OF_DECLARE type driver. Because of
that, TTC driver may be initialized before other clock drivers. If
TTC driver is dependent on that clock driver then initialization of
TTC driver will failed.

So use TTC driver as platform driver instead of using
TIMER_OF_DECLARE.

Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1573122988-18399-1-git-send-email-rajan.vaja@xilinx.com