[QEMU] add support for seco-qemuarm-imx and seco-qemuarm64-imx
- add missing Kconfig entry (SYS_EARLY_PCI_INIT)
- fix the defconfigs so that they load env and kernel from sd card
- set correct offsets in defconfigs
- use booti for aarch64 and bootz for arm
- add seco environment in both machines
- do not relocate initramfs (not necessary and the default address is invalid)