hwspinlock: omap: Use devm_pm_runtime_enable() helper

hwspinlock: omap: Use devm_pm_runtime_enable() helper

This disables runtime PM on module exit automatically for us, currently
we manually disable runtime PM which can be error-prone if not done
in the right order or missed in some exit path. This also allows us
to simplify the probe exit path and remove callbacks. Do that here.

While here, as we can now return right after registering our hwspinlock,
simply return directly and remove the extra debug message.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240208165114.63148-2-afd@ti.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>