arm: imx8mp-phycore: move to OF_UPSTREAM

The PHYCORE_IMX8MP is used by the phyBOARD-Pollux. Migrate board to
OF_UPSTREAM. Linux kernel device tree for the board can be used as is,
corresponding U-Boot device tree files are removed. U-Boot tweaks are
kept unchanged.

Signed-off-by: Yannic Moog <y.moog@phytec.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Teresa Remmet <t.remmet@phytec.de>
diff --git a/configs/phycore-imx8mp_defconfig b/configs/phycore-imx8mp_defconfig
index 9f42edd..7b16e8e 100644
--- a/configs/phycore-imx8mp_defconfig
+++ b/configs/phycore-imx8mp_defconfig
@@ -9,7 +9,7 @@
 CONFIG_ENV_OFFSET=0x3C0000
 CONFIG_SYS_I2C_MXC_I2C1=y
 CONFIG_DM_GPIO=y
-CONFIG_DEFAULT_DEVICE_TREE="imx8mp-phyboard-pollux-rdk"
+CONFIG_DEFAULT_DEVICE_TREE="freescale/imx8mp-phyboard-pollux-rdk"
 CONFIG_SPL_TEXT_BASE=0x920000
 CONFIG_TARGET_PHYCORE_IMX8MP=y
 CONFIG_PHYTEC_SOM_DETECTION=y