drm/komeda: Add ACLK rate to sysfs

Expose node with the name 'aclk_hz'

Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Ayan kumar halder <ayan.halder@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190828110342.45936-1-mihail.atanassov@arm.com