clocksource/drivers/timer-ti-dm: Move struct omap_dm_timer fields to driver

clocksource/drivers/timer-ti-dm: Move struct omap_dm_timer fields to driver

There is no longer any need to expose the elements of struct omap_dm_timer
outside the driver. The pwm and remoteproc drivers just use struct
omap_dm_timer as a cookie.

Let's move the elements of struct omap_dm_timer into struct dmtimer that
is private to the driver. To do this, we mostly rename omap_dm_timer to
dmtimer in the driver. We keep omap_dm_timer only for the exposed
functions in the platform_data for the pwm and remoteproc drivers.

Let's also add a note about not using the exposed functions internally as
those will get deprecated eventually in favor of Linux generic frameworks.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Link: https://lore.kernel.org/r/20220815131250.34603-8-tony@atomide.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>