MAINTAINERS: EDAC/armada_xp: include dt-bindings

Include dt-bindings for Marvell Armada XP SDRAM in the EDAC-ARMADA
entry.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210817093807.59531-2-krzysztof.kozlowski@canonical.com