ARM: mach-shmobile: default to no earlytimer

Now when all SoCs and boards are converted to use
shmobile_earlytimer_init(), change the default behavior
of shmobile_timer.init() from using early timer to
do nothing which is suitable for upcoming DT support.

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