fix(imx8mq): correct architected counter frequency

Different from other i.MX SoCs, which typically use a 24MHz reference clock,
the i.MX8MQ uses a 25MHz reference clock. As the architected timer clock
frequency is directly sourced from the reference clock via a /3 divider this
SoC runs the timers at 8.33MHz.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Change-Id: Ief36af9ffebce7cb75a200124134828d3963e744