ARM: mach-shmobile: sh7372, AP4EVB and Mackerel timer rework

Move the SoC specific timer code from AP4EVB and Mackerel
to sh7372 setup code. This makes is possible to share
the SoC specific timer code across boards and it also
removes the need for a board specific timer structure.

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