ARM: mach-shmobile: Use CMT2 for timer on sh7372

Switch the sh7372 CPU support to use CMT2 instead
of CMT1 for system timer.

CMT1 is located in the A3SP power domain while CMT2
is located in the always-on power domain C5.

This improves our PM situation - with CMT2 as timer
we can power down A3SP and still access the timer.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>