clocksource: Select CLKSRC_MMIO where needed

clocksource: Select CLKSRC_MMIO where needed

The Tegra clocksource implementation uses the clocksource_mmio helper
functions, but currently can be configured without them, which fails:

drivers/clocksource/built-in.o: In function `tegra20_init_timer':
:(.init.text+0xac): undefined reference to `clocksource_mmio_init'
:(.init.text+0x140): undefined reference to `clocksource_mmio_readl_up'

The same problem exists for Digicolor:

drivers/clocksource/built-in.o: In function `digicolor_timer_init':
:(.init.text+0xfa): undefined reference to `clocksource_mmio_init'
:(.init.text+0x14c): undefined reference to `clocksource_mmio_readl_down'

I've inspected the Kconfig file to look for other cases that I have not
yet run into, and added an explicit 'select' to each one to ensure we
can successfully link the drivers.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: http://lkml.kernel.org/r/1453737776-1960372-1-git-send-email-arnd@arndb.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>