MAINTAINERS: add an entry for AMD DC DML

We want all DML changes to be reviewed by Chaitanya or Jun. So, add an
entry for DML to MAINTAINERS.

Suggested-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240703191341.239296-1-hamza.mahfooz@amd.com