clocksource: Add Kconfig entries for CMT, MTU2, TMU and STI

Add Kconfig entries for CMT, MTU2, TMU and STI to
drivers/clocksource/Kconfig. This will allow us to
get rid of duplicated entires in architecture code
such as arch/sh and arch/arm/mach-shmobile.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Wolfram Sang <wsa@sang-engineering.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>