PM / shmobile: Make TMU driver use pm_genpd_dev_always_on()

Make the TMU clocksource driver mark its device as "always on"
using pm_genpd_dev_always_on() to protect it from surprise power
removals and make sh7372_add_standard_devices() add TMU devices on
sh7372 to the A4R power domain so that their "always on" flags
are taken into account as appropriate.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Tested-by: Simon Horman <horms@verge.net.au>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Cc: stable@vger.kernel.org