mshv: Add support for integrated scheduler

Query the hypervisor for integrated scheduler support and use it if
configured.

Microsoft Hypervisor originally provided two schedulers: root and core. The
root scheduler allows the root partition to schedule guest vCPUs across
physical cores, supporting both time slicing and CPU affinity (e.g., via
cgroups). In contrast, the core scheduler delegates vCPU-to-physical-core
scheduling entirely to the hypervisor.

Direct virtualization introduces a new privileged guest partition type - L1
Virtual Host (L1VH) — which can create child partitions from its own
resources. These child partitions are effectively siblings, scheduled by
the hypervisor's core scheduler. This prevents the L1VH parent from setting
affinity or time slicing for its own processes or guest VPs. While cgroups,
CFS, and cpuset controllers can still be used, their effectiveness is
unpredictable, as the core scheduler swaps vCPUs according to its own logic
(typically round-robin across all allocated physical CPUs). As a result,
the system may appear to "steal" time from the L1VH and its children.

To address this, Microsoft Hypervisor introduces the integrated scheduler.
This allows an L1VH partition to schedule its own vCPUs and those of its
guests across its "physical" cores, effectively emulating root scheduler
behavior within the L1VH, while retaining core scheduler behavior for the
rest of the system.

The integrated scheduler is controlled by the root partition and gated by
the vmm_enable_integrated_scheduler capability bit. If set, the hypervisor
supports the integrated scheduler. The L1VH partition must then check if it
is enabled by querying the corresponding extended partition property. If
this property is true, the L1VH partition must use the root scheduler
logic; otherwise, it must use the core scheduler. This requirement makes
reading VMM capabilities in L1VH partition a requirement too.

Signed-off-by: Andreea Pintilie <anpintil@microsoft.com>
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>