ARM: mach-shmobile: r8a7740 and Bonito timer rework

Copy the SoC specific timer code from Bonito board code
to r8a7740 setup code. This makes is possible to share
the SoC specific timer code across boards. The Bonito
specific timer setup code tied to the FPGA is kept as-is.

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