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/arch/arm/mach-imx/imx8m/Kconfig b/arch/arm/mach-imx/imx8m/Kconfig
index f81be42..046c785 100644
--- a/arch/arm/mach-imx/imx8m/Kconfig
+++ b/arch/arm/mach-imx/imx8m/Kconfig
@@ -303,6 +303,7 @@
 	select IMX8MP
 	select SUPPORT_SPL
 	select IMX8M_LPDDR4
+	imply OF_UPSTREAM
 
 config TARGET_IMX8MM_CL_IOT_GATE
 	bool "CompuLab iot-gate-imx8"