clock_control: Add support for getting LPO frequency in mcux sim driver

The mcux sim clock control driver was originally designed to pass
through the clock subsystem value from dts to the mcux CLOCK_GetFreq()
function. This assumed that the values in
include/dt-bindings/clock/kinetis_sim.h matched the enumeration in
fsl_clock.h, which is true for the coresys, platform, and bus clocks.
However, the low-power oscillator (LPO) clock has a different values in
k64 vs. kw2xd, therefore we must update the clock_control driver to
parse the value from dts and convert it to the fsl_clock.h enumeration.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>