qemu: Formally deprecate support for qemu < 3.1

As of April 23 2022, Ubuntu 20.04 will be out for two years, which means
we no longer have to support Ubuntu 18.04 along with qemu-2.11 shipped
with it.

This then brings the minimum qemu version we have to support to
qemu-3.1:

   Debian 10/Stable: 3.1
 OpenSUSE Leap 15.3: 5.2
       Ubuntu 20.04: 4.2
    RHEL/Centos 8.4: 4.2

Next event in this space will be 2023/07/06 when Debian 11 will be out
for two years.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

docs/drvqemu.rst

@@ -5,7 +5,7 @@
 QEMU/KVM/HVF hypervisor driver
 ==============================
 
-The libvirt KVM/QEMU driver can manage any QEMU emulator from version 2.11.0 or
+The libvirt KVM/QEMU driver can manage any QEMU emulator from version 3.1.0 or
 later.
 
 It supports multiple QEMU accelerators: software
@@ -34,8 +34,8 @@ Deployment pre-requisites
    ``qemu-kvm`` and ``/dev/kvm`` device node. If both are found, then KVM fully
    virtualized, hardware accelerated guests will be available.
 -  **Hypervisor.framework (HVF)**: The driver will probe ``sysctl`` for the
-   presence of ``Hypervisor.framework``. If it is found and QEMU is newer than
-   2.12, then it will be possible to create hardware accelerated guests.
+   presence of ``Hypervisor.framework``. If it is found it will be possible to
+   create hardware accelerated guests.
 
 Connections to QEMU driver
 --------------------------

src/qemu/qemu_capabilities.c

@@ -5381,8 +5381,8 @@ virQEMUCapsProbeQMPSchemaCapabilities(virQEMUCaps *qemuCaps,
     return 0;
 }
 
-#define QEMU_MIN_MAJOR 2
-#define QEMU_MIN_MINOR 11
+#define QEMU_MIN_MAJOR 3
+#define QEMU_MIN_MINOR 1
 #define QEMU_MIN_MICRO 0
 
 virDomainVirtType