meta-agl-bsp: update virtio-aarch64

meta-agl-bsp: update virtio-aarch64

Updates to get the virtio-aarch64 machine building after the
upgrade to Yocto Project 4.0 / kirkstone:
- Switch to the 5.15 linux-yocto kernel and drop the local backport
  of the 5.10 recipe.
- Fix override syntax in the machine-specific linux-yocto bbappend.
- Remove all the patches applied for the virtio and virtio-snd
  configuration fragments, they seem to have all been applied
  upstream.

Bug-AGL: SPEC-4356

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I96d4bb9b04d74280d1a3767fe17284fe6049fcba
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/27465
Reviewed-by: Vasyl Vavrychuk <vasyl.vavrychuk@opensynergy.com>
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account