board: phytec: phycore_imx8mp: Add 4000MTS RAM timings based on PCB rev

Starting with PCB revision 3 we can safely make use of higher RAM
frequency again. Make use of the EEPROM detection to determine the
revision and use the updated RAM timings for new SoMs.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Reviewed-by: Yannic Moog <y.moog@phytec.de>
Tested-by: Yannic Moog <y.moog@phytec.de>