This function was intended for MN2WS0235 (what we call PH1-Pro4TV).
On that SoC, MPLL is already running on the power-on reset and it
makes sense to stop the PLL at early boot-up.
On the other hand, PH1-Pro4(R) does not have SC_MPLLOSCCTL register,
so this function has no point.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>