Update to QEMU 5.2

Lots of patches touched and some slight changes to the build process
since QEMU switched to meson as their build system. Functionality-wise
very little rebasing required.

New patches introduced:
* pve/0058: to fix VMA backups and clean up some code in general with
  new 5.2 features now available to us (namely coroutine-enabled QMP).
* extra/0002: don't build man pages for guest agent when disabled
* extra/0003: fix live-migration with hugepages
* 0017 and 0018 are adjusted to fix snapshot abort and improve
  snap performance a bit

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

debian/patches/pve/0023-PVE-monitor-disable-oob-capability.patch

@@ -18,10 +18,10 @@ Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  1 file changed, 1 insertion(+), 2 deletions(-)
 
 diff --git a/monitor/qmp.c b/monitor/qmp.c
-index d433ceae5b..a16cf3532d 100644
+index b42f8c6af3..2e37d11bd3 100644
 --- a/monitor/qmp.c
 +++ b/monitor/qmp.c
-@@ -409,8 +409,7 @@ void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp)
+@@ -466,8 +466,7 @@ void monitor_init_qmp(Chardev *chr, bool pretty, Error **errp)
      qemu_chr_fe_set_echo(&mon->common.chr, true);
  
      /* Note: we run QMP monitor in I/O thread when @chr supports that */