ARM: shmobile: Set PM domain on/off latencies directly

The results of adaptive latency computations in __pm_genpd_poweron()
and pm_genpd_poweroff() show that the power on/power off latencies
of all power domains in SH7372 are a little below 250 us.  Therefore,
if 250 us is used as the common initial value of the latency fields
in struct generic_pm_domain for all domains, the latency values
will never have to change at run time and there won't be any overhead
related to re-computation of the corresponding PM QoS data.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Magnus Damm <damm@opensource.se>