ARM: stm32: Update MAINTAINERS file globs for STM32MP DHSOM

Update the MAINTAINERS file glob to cover all of STM32MP DHSOM related files.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>