PM / shmobile: Remove the stay_on flag from SH7372's PM domains

SH7372 uses two independent mechanisms for ensuring that power
domains will never be turned off: the stay_on flag and the "always
on" domain governor.  Moreover, the "always on" governor is only taken
into accout by runtime PM code paths, while the stay_on flag affects
all attempts to turn the given domain off.  Thus setting the stay_on
flag causes the "always on" governor to be unnecessary, which is
quite confusing.

However, the stay_on flag is currently only set for two domains: A3SP
and A4S.  Moreover, it only is set for the A3SP domain if
console_suspend_enabled is set, so stay_on won't be necessary for
that domain any more if console_suspend_enabled is checked directly
in its .suspend() routine.  [This requires domain .suspend() to
return a result, but that is a minor modification.]  Analogously,
stay_on won't be necessary for the A4S domain if it's .suspend()
routine always returns an error code.

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