boards: arm: stm32: enable pinctrl driver

Enable the pin control driver on all STM32 based boards. The following
script has been used to do this task:

```
from pathlib import Path
import re

for fpath in Path(".").glob("boards/arm/**/*_defconfig"):
    lines = open(fpath).readlines()

    is_stm32 = False
    for line in lines:
        if "CONFIG_SOC_SERIES_STM32" in line:
            is_stm32 = True
            break

    if not is_stm32:
        continue

    lines += ["\n", "# enable pin controller\n", "CONFIG_PINCTRL=y\n"]

    with open(fpath, "w") as f:
        f.writelines(lines)
```

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>