ap-common: Switch to Linux 6.1 by default on x86 + drop dom0 i386

ap-common: Switch to Linux 6.1 by default on x86 + drop dom0 i386

linux-4.19 branch in xenbits is outdated, it haven't been updated and
tested since 2020 as it has been disabled in osstest. Also, this 4.19
branch doesn't build on Bookworm.

So we will start to use a newer version of Linux. We switch to 6.1 for
the Arm* tests recently, so will use that same version for x86.

Also, following commit 3a3089c94913 ("mfi-common: Drop Linux dom0 i386
tests for newer Linux branches"), 32bit dom0 isn't tested on newer
Linux, so we need to drop all dom0 i386 tests wherever the default
linux branch is used. That is, this changes in jobs will apply to
"xen-unstable" branch but also all xen stable branches, seabios, qemu,
osstest, libvirt, so every branch that aren't "linux-*".

Here is the list jobs that changes, and whether they are replace, or
have existing equivalents, on the "xen-unstable" branch. Changes
compared with:
    OSSTEST_CONFIG=standalone-config-example nice eatmydata ./standalone-generate-dump-flight-runvars

Gone, without exiting or new test-amd64-amd64-*:
- test-amd64-i386-freebsd10-amd64
- test-amd64-i386-freebsd10-i386
- test-amd64-i386-qemut-rhel6hvm-amd
- test-amd64-i386-qemut-rhel6hvm-intel
- test-amd64-i386-qemuu-rhel6hvm-amd
- test-amd64-i386-qemuu-rhel6hvm-intel

Gone, but with exiting test-amd64-amd64-* equivalent:
- test-amd64-coresched-i386-xl
- test-amd64-i386-examine
- test-amd64-i386-examine-bios
- test-amd64-i386-examine-uefi
- test-amd64-i386-libvirt
- test-amd64-i386-libvirt-pair
- test-amd64-i386-libvirt-qemuu-debianhvm-amd64-xsm
- test-amd64-i386-libvirt-xsm
- test-amd64-i386-livepatch
- test-amd64-i386-migrupgrade
- test-amd64-i386-pair
- test-amd64-i386-xl
- test-amd64-i386-xl-pvshim
- test-amd64-i386-xl-qemut-debianhvm-amd64
- test-amd64-i386-xl-qemut-debianhvm-i386-xsm
- test-amd64-i386-xl-qemut-stubdom-debianhvm-amd64-xsm
- test-amd64-i386-xl-qemut-win7-amd64
- test-amd64-i386-xl-qemut-ws16-amd64
- test-amd64-i386-xl-qemuu-debianhvm-amd64
- test-amd64-i386-xl-qemuu-debianhvm-amd64-shadow
- test-amd64-i386-xl-qemuu-debianhvm-i386-xsm
- test-amd64-i386-xl-qemuu-dmrestrict-amd64-dmrestrict
- test-amd64-i386-xl-qemuu-ovmf-amd64
- test-amd64-i386-xl-qemuu-win7-amd64
- test-amd64-i386-xl-qemuu-ws16-amd64
- test-amd64-i386-xl-shadow
- test-amd64-i386-xl-simplat-amd64-buster
- test-amd64-i386-xl-xsm

Gone, but replaced by a new test-amd64-amd64-*:
- test-amd64-i386-libvirt-qcow2
- test-amd64-i386-libvirt-raw
- test-amd64-i386-xl-vhd
+ test-amd64-amd64-libvirt-qcow2
+ test-amd64-amd64-libvirt-raw
+ test-amd64-amd64-xl-vhd

In any case, the list of test would be the same as for the existing
branch "linux-linus" or "linux-6.1" branches.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Juergen Gross <jgross@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>