board: phytec: phycore_imx8mp: Add support for different RAM sizes

board: phytec: phycore_imx8mp: Add support for different RAM sizes

Add support for different RAM sizes and speed grades on the
phyCORE-i.MX8MP.
Add support for 1GB 1.5GHz, 1GB 2GHz, 4GB 1.5GHz,
4GB 2GHz and 8GB 2GHz RAM.
The RAM size and speed grade is detected by the information
stored in the EEPROM on the SoM.

Co-developed-by: Benjamin Hahn <B.Hahn@phytec.de>
Signed-off-by: Benjamin Hahn <B.Hahn@phytec.de>
Co-developed-by: Yannic Moog <y.moog@phytec.de>
Signed-off-by: Yannic Moog <y.moog@phytec.de>
Co-developed-by: Yashwanth Varakala <y.varakala@phytec.de>
Signed-off-by: Yashwanth Varakala <y.varakala@phytec.de>
Signed-off-by: Teresa Remmet <t.remmet@phytec.de>