Runtime power management support breaks Intel LTE modem where dmesg dump
showes timeout errors:

```
[   72.027442] iosm 0000:01:00.0: msg timeout
[   72.531638] iosm 0000:01:00.0: msg timeout
[   73.035414] iosm 0000:01:00.0: msg timeout
[   73.540359] iosm 0000:01:00.0: msg timeout
```

Furthermore, when shutting down with `poweroff` and modem attached, the
system rebooted instead of powering down as expected. The modem works
again only after power cycling.

Revert runtime power management support for IOSM driver as introduced by
commit e4f5073d ("net: wwan: iosm: enable runtime pm support for
7560").

Fixes: e4f5073d ("net: wwan: iosm: enable runtime pm support for 7560")
Reported-by: Martin <mwolf@adiumentum.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217996
Link: https://lore.kernel.org/r/267abf02-4b60-4a2e-92cd-709e3da6f7d3@gmail.com/Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>