accel/mshv: Add vCPU creation and execution loop

accel/mshv: Add vCPU creation and execution loop

Create MSHV vCPUs using MSHV_CREATE_VP and initialize their state.
Register the MSHV CPU execution loop loop with the QEMU accelerator
framework to enable guest code execution.

The target/i386 functionality is still mostly stubbed out and will be
populated in a later commit in this series.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-11-magnuskulke@linux.microsoft.com
[Fix g_free/g_clear_pointer confusion; rename qemu_wait_io_event;
 mshv.h/mshv_int.h split. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>