PM / devfreq: Drop explicit selection of PM_OPP

CONFIG_PM_OPP is already selected by CONFIG_PM_DEVFREQ
since commit b9c69e04

 ("PM / devfreq: Add dependency on PM_OPP").
This means that individual drivers shouldn't "select PM_OPP" explicitly.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
[cw00.choi: Edit the patch title]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>