PM / devfreq: Remove "select SRCU"

Now that the SRCU Kconfig option is unconditionally selected, there is
no longer any point in selecting it.  Therefore, remove the "select SRCU"
Kconfig statements.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/devfreq/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 menuconfig PM_DEVFREQ
 	bool "Generic Dynamic Voltage and Frequency Scaling (DVFS) support"
-	select SRCU
 	select PM_OPP
 	help
 	  A device may have a list of frequencies and voltages available.