clocksource/drivers/exynos_mct: Support frc-shared property

When the FRC is shared with another main processor, the other processor
is assumed to have started it and this processor should not write to the
global registers.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220609112738.359385-3-vincent.whitchurch@axis.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>