KVM x86 misc changes for 6.10:

 - Advertise the max mappable GPA in the "guest MAXPHYADDR" CPUID field, which
   is unused by hardware, so that KVM can communicate its inability to map GPAs
   that set bits 51:48 due to lack of 5-level paging.  Guest firmware is
   expected to use the information to safely remap BARs in the uppermost GPA
   space, i.e to avoid placing a BAR at a legal, but unmappable, GPA.

 - Use vfree() instead of kvfree() for allocations that always use vcalloc()
   or __vcalloc().

 - Don't completely ignore same-value writes to immutable feature MSRs, as
   doing so results in KVM failing to reject accesses to MSR that aren't
   supposed to exist given the vCPU model and/or KVM configuration.

 - Don't mark APICv as being inhibited due to ABSENT if APICv is disabled
   KVM-wide to avoid confusing debuggers (KVM will never bother clearing the
   ABSENT inhibit, even if userspace enables in-kernel local APIC).