ARM: clocksource: Initialise early

ARM: clocksource: Initialise early

Initialise clock sources early, since some subsystems rely on them to
initialize.

This came up when working on DT support for the kzm9g board.
The prototype does not use early timers and I found that the
CMT clocksource needs to be initialised before the MMCIF MMC driver.

Cc: linux-kernel@vger.kernel.org
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>