MAINTAINERS: add Conor as a dt-bindings maintainer

Rob asked if I would be interested in helping with the dt-bindings
maintenance, and since I am a glutton for punishment I accepted.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230504-renderer-alive-1c01d431b2a7@spud
Signed-off-by: Rob Herring <robh@kernel.org>