meta-agl-kvm-demo: Add initial Raspberry Pi support

meta-agl-kvm-demo: Add initial Raspberry Pi support

Changes:
- Add Rasperry Pi specific agl-qemu-runner configuration files for
  the KVM demo guests.  These have only been tested on a 8 GB RPi 5;
  it is possible that the USB port configuration for passing through
  the touchscreen may need tweaking for RPi 4, this will be addressed
  in follow up changes if required.  There is some potential for
  tweaking the guest memory configurations to try to run on 4 GB
  hardware, but that will likely take some more rework of the
  configuration system.
- Replace the duplicated agl-qemu-runner configuration files for the
  reference hardware with symlinks to clean things up a bit.
- To work around what seems like a detection problem in libepoxy
  that leads to a crash, tweak agl-qemu-runner to explicitly pass
  "gl=es" for the QEMU SDL display option by default (instead of the
  previous "gl=on").  A hook variable has been left to allow
  overriding this in a guest configuration.

Bug-AGL: SPEC-5305

Change-Id: I6270b7d96164a7f8e756660e733d1285d22b621e
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/30720
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-boot-test: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
Tested-by: Jenkins Job builder account