Raspberry 4: XEN support

Raspberry 4: XEN support

Added the support for DOM0 in raspberry pi4. The feature agl-virt-xen should be enabled to activate this code.

1512 MB of memory is used for DOM0 machine.

There are limitations:
	- brcmfmac module disabled (bluethooth and Wifi) due to the crash
	- total_memory is set to the 3Gb, as it impacts the USB ports on rasbperry pi4 on Linux kernel 4.19

v2 (jsmoeller): make changes in virtualization-layer conditional to raspberrypi4

Bug-AGL: SPEC-3259
Change-Id: I873fbf1f5498e31ae5f468407502f16e1873f7fc
Signed-off-by: Leonid Lazarev <leonid.lazarev@mera.com>
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/24522
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>