PM / devfreq: imx8m-ddrc: Remove unused defines

The IMX_SIP_DDR_DVFS_WAIT_CHANGE and IMX_SIP_DDR_FREQ_SET_HIGH defines
are not used so they can be removed.

Fixes: 518e99e2a22e ("PM / devfreq: Add dynamic scaling for imx8m ddr controller")
Reported-by: Shawn Guo <shawn.guo@kernel.org>
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>