dt-bindings: reserved-memory: Add support for DRAM MRQ GSCs

Add bindings for DRAM MRQ GSC support.

Co-developed-by: Stefan Kristiansson <stefank@nvidia.com>
Signed-off-by: Stefan Kristiansson <stefank@nvidia.com>
Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>