default or selected kernelversion does not have config value CONFIG_REGULATOR_ST_PWM.
Result is shown for kernelversion 6.4.14

STMicroelectronics PWM voltage regulator

modulename: st-pwm.ko

configname: CONFIG_REGULATOR_ST_PWM

Linux Kernel Configuration
└─>Device Drivers
└─>Voltage and Current Regulator Support
└─>STMicroelectronics PWM voltage regulator
In linux kernel since version 3.15 (release Date: 2014-06-08)  
This driver supports ST's PWM controlled voltage regulators.

source code:
drivers/regulator/st-pwm.c