soc: mimxrt685s/hifi4: Fix HW cycle count

Change hardware cycle count (CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC) to 594
MHz. Move that value to the SoC layer's DT.

Validated with the amp_blinky example - the period of the blinking LED
is exactly 2 seconds, like was programmed.

Signed-off-by: Vit Stanicek <vit.stanicek@nxp.com>