ARM: dts: imx: fix IPU OF graph endpoint node names

OF graph endpoint nodes are supposed to be named 'endpoint' with an
address if there is more than one. The i.MX IPU binding graph has used
unique endpoint names instead which now generate dtc warnings:

Warning (graph_endpoint): /soc/ipu@2400000/port@2/disp0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@2/hdmi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@2/mipi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@2/lvds0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@2/lvds1-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@3/disp1-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@3/hdmi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@3/mipi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@3/lvds0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2400000/port@3/lvds1-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@2/disp0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@2/hdmi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@2/mipi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@2/lvds0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@2/lvds1-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@3/hdmi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@3/mipi-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@3/lvds0-endpoint: graph endpont node name should be 'endpoint'
Warning (graph_endpoint): /soc/ipu@2800000/port@3/lvds1-endpoint: graph endpont node name should be 'endpoint'

Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>