PM: runtime: Unify error handling during suspend and resume

There is a confusing difference in error handling between rpm_suspend()
and rpm_resume() related to the special way in which -EAGAIN and -EBUSY
error values are treated by the former.  Also, converting -EACCES coming
from the callback to I/O error, which it quite likely is not, may
confuse runtime PM users.

To address the above, modify rpm_callback() to convert -EACCES coming
from the driver to -EAGAIN and to set power.runtime_error only if the
return value is not -EAGAIN or -EBUSY.

This will cause the error handling in rpm_resume() and rpm_suspend() to
work consistently, so drop the no longer needed -EAGAIN or -EBUSY
special case from the latter and make it retry autosuspend if
power.runtime_error is unset.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/12620037.O9o76ZdvQC@rjwysocki.net