ARM: mach-shmobile: sh7377 and G4EVM timer rework

Move the SoC specific timer code from G4EVM board code
to sh7377 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>