clocksource/drivers/timer-imx-tpm: Convert the driver to timer-of

Convert the driver to use the timer_of helpers.  This allows to handle
timer base, clock and irq using common timer_of driver and it
simplifies the code.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>