MAINTAINERS: Update entry for DH electronics DHSOM SoMs and boards

MAINTAINERS: Update entry for DH electronics DHSOM SoMs and boards

Update the MAINTAINERS entry to cover all DH electronics DHSOM
SoMs and boards. The DHSOM is the name which covers all modules,
DHCOM is the SODIMM seated SoM, DHCOR is the solder on module.
Use glob pattern to match on every DT file which contains either
of those three module substrings in lowercase.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>