accel/mshv: Initialize VM partition

accel/mshv: Initialize VM partition

Create the MSHV virtual machine by opening a partition and issuing
the necessary ioctl to initialize it. This sets up the basic VM
structure and initial configuration used by MSHV to manage guest state.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-10-magnuskulke@linux.microsoft.com
[Add stubs; fix format strings for trace-events; make mshv_hvcall
 available only in per-target files; mshv.h/mshv_int.h split. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>