[QEMU] add support for seco-qemuarm-imx seco-qemuarm64-imx
Add support for new machines (QEMU ARMv7/v8 virt with SECO i.MX BSP). Specifically:
- add rauc configuration file
- add fw-env config file (reuse i.MX6 for arm, i.MX8 for aarch64)
- add U-boot script
- use qemuarm wks template