Since __imx_cpu_type won't be initialized until
imx_init()@postcore_initcall is executed cpu_is_mx8mq() will only work
correctly at core_initcall level so long as imx_cpu_type does not
resolve into __imx_cpu_type. This is currently the case and
imx8mq_init_syscnt_frequency() works as expected, but it probably
won't be in the future.

To avoid this problem introduce imx8mq_cpu_lowlevel_init() and do
system counter frequency initialization there. Also convert all of the
i.MX8MQ boards to use this new function.

Fixes: 5691aed9a ("ARM: i.MX8MQ: Check CPU type in imx8mq_init_syscnt_frequency()")
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>