Raspberry 4: XEN support

1) We've found the workaround for xen, to allow RPI4 to allocate limited memory size for dom0 (for example only 1 Gb) with full capacity of the memory (up to 3 GB). So, it is possible to use several GBs of memory for domUs.
It is implemented for Ubuntu by us in https://github.com/mera-company/rpi4-xen-uboot.

2) We can not use up to 4 Gb, due to limitation for USB. USB works only with 3GB of total mem. it is known issues for raspberry PI4

3) We still have issue with wifi. Wifi driver crashes under xen.

4) On Ubuntu, we got HDMI working with this configuration
5) We plan to integrate this solution on AGL with u-boot loading with known limitations

Good progress! Keep us updated.

Status: We took the https://github.com/dornerworks/xen-rpi4-builder as base.
The memory for Rasp has been increased to 4G, dom0_mem has been increased to 3Gb.

At this moment we were able to load AGL under XEN on raspberry without HDMI and without brcmfmac module (WIFI support).

Both HDMI and brcmfmac loading lead to crash at the moment. Investigation is in progress