scripts: genpinctrl: add MCO to pinctrl generation config

This commit adds MCO to the configuration file for
pinctrl generation.
The match regex was base upon the result of running the command:

git grep Name=\"RCC_MCO | cut -d \" -f2 | sort | uniq

in the STM32_open_pin_data repository giving the following:

RCC_MCO
RCC_MCO_1
RCC_MCO_2

Signed-off-by: Benjamin Björnsson <benjamin.bjornsson@gmail.com>