boards: nxp: frdm_ke17z512: update dts to update bus_clk divider

Update the bus_clk divider value from 4 to 2 for frdm_ke17z512
platform. The bus and flash clocks are raised to 16Mhz to ensure
that `tests.kernel.timer.timer_jitter_drift` sample passes.

Signed-off-by: Anke Xiao <anke.xiao@nxp.com>