CODEOWNERS: update for stm32 arch, drivers, dts and disco_l475_iot1

Add codeowners for:
arch/arm/soc/st_stm32
drivers/*/*stm32*
dts/arm/st
boards/arm/disco_l475_iot1

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
1 file changed