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/0004-PVE-Config-ui-spice-default-to-pve-certificates.patch

@@ -9,10 +9,10 @@ Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  1 file changed, 9 insertions(+), 6 deletions(-)
 
 diff --git a/ui/spice-core.c b/ui/spice-core.c
-index ecc2ec2c55..ca04965ead 100644
+index eea52f5389..d09ee7f09e 100644
 --- a/ui/spice-core.c
 +++ b/ui/spice-core.c
-@@ -668,32 +668,35 @@ void qemu_spice_init(void)
+@@ -667,32 +667,35 @@ static void qemu_spice_init(void)
  
      if (tls_port) {
          x509_dir = qemu_opt_get(opts, "x509-dir");