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>
6 files changed