dt-bindings: remove Joonyoung Shim from maintainers

Emails to Joonyoung Shim bounce ("550 5.1.1 Recipient address rejected:
User unknown"), so remove him from maintainers of DT bindings (display,
phy).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>