*i386/sev: add experimental 'discard' option for SEV guests

This adds an sev-guest/sev-snp-guest object parameter to control how to
handle discarding of backing memory after a shared<->private conversion.

This may eventually be useful upstream in some form, but for now it is
mainly to help identity bottlenecks or workaround known ones (like OVMF
DMA buffers) to test other aspects of performance.

Signed-off-by: Michael Roth <michael.roth@amd.com>

qemu-ga patch queue for hard-freeze

* fix memory leak in guest_exec

qemu-ga patch queue for hard-freeze

* w32: Fix missing/incorrect DLLs in MSI installer
* w32: Fix memory leaks in guest-get-osinfo/guest-get-fsinfo
* w32: Increase timeout for guest-fsfreeze-freeze

qemu-ga patch queue for soft-freeze

* add support for Windows Server 2022 in get-osinfo command

qemu-ga patch queue for soft-freeze

* fix guest-get-vcpus reporting after vcpu unplug
* coding style fix-ups
* report a reason for disabled commands

qemu-ga patch queue for hard-freeze

* fixes for schema data-type declarations for guest-get-disks

qemu-ga patch queue for hard-freeze

* fix leaked DIR* descriptor in guest-get-disks spotted by coverity

qemu-ga patch queue for soft-freeze

* add guest-get-disks for w32/linux
* add guest-{add,remove,get}-authorized-keys
* fix API violations and schema documentation inconsistencies with
  recently-added guest-get-devices

v3:
- fix checkpatch errors regarding disallowed usages of g_assert*
  macros and other warnings

v2:
- fix BSD build error due to missing stub for guest_get_disks
- fix clang build error on linux due to unused variable
- disable qga-ssh-test for now due to a memory leak within GLib when
  G_TEST_OPTION_ISOLATE_DIRS is passed to g_test_init() since it
  break Gitlab CI build-oss-fuzz test
- rebased and re-tested on master

qemu-ga patch queue for soft-freeze

* add guest-get-disks for w32/linux
* add guest-{add,remove,get}-authorized-keys
* fix API violations and schema documentation inconsistencies with
  recently-added guest-get-devices

v2:
- fix BSD build error due to missing stub for guest_get_disks
- fix clang build error on linux due to unused variable
- disable qga-ssh-test for now due to a memory leak within GLib when
  G_TEST_OPTION_ISOLATE_DIRS is passed to g_test_init() since it
  break Gitlab CI build-oss-fuzz test
- rebased and re-tested on master

qemu-ga patch queue for soft-freeze

* add guest-get-disks for w32/linux
* add guest-{add,remove,get}-authorized-keys
* fix API violations and schema documentation inconsistencies with
  recently-added guest-get-devices