rockchip: rk3368: spl: define COUNTER_FREQUENCY to 24MHz

rockchip: rk3368: spl: define COUNTER_FREQUENCY to 24MHz

The BootROM of the RK3368 Boot ROM does not initialise cntfrq_el0.
This change defines COUNTER_FREQUENCY, which is used by the AArch64 init
code in arch/arm/cpu/armv8/start.S to set up cntfrq_el0.

If the counter-frequency is not correctly set up, the calculation of
delays using the ARMv8 generic timer can not work correctly.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>