KVM: Move coalesced MMIO initialization (back) into kvm_create_vm()

KVM: Move coalesced MMIO initialization (back) into kvm_create_vm()

Invoke kvm_coalesced_mmio_init() from kvm_create_vm() now that allocating
and initializing coalesced MMIO objects is separate from registering any
associated devices.  Moving coalesced MMIO cleans up the last oddity
where KVM does VM creation/initialization after kvm_create_vm(), and more
importantly after kvm_arch_post_init_vm() is called and the VM is added
to the global vm_list, i.e. after the VM is fully created as far as KVM
is concerned.

Originally, kvm_coalesced_mmio_init() was called by kvm_create_vm(), but
the original implementation was completely devoid of error handling.
Commit 6ce5a090a9a0 ("KVM: coalesced_mmio: fix kvm_coalesced_mmio_init()'s
error handling" fixed the various bugs, and in doing so rightly moved the
call to after kvm_create_vm() because kvm_coalesced_mmio_init() also
registered the coalesced MMIO device.  Commit 2b3c246a682c ("KVM: Make
coalesced mmio use a device per zone") cleaned up that mess by having
each zone register a separate device, i.e. moved device registration to
its logical home in kvm_vm_ioctl_register_coalesced_mmio().  As a result,
kvm_coalesced_mmio_init() is now a "pure" initialization helper and can
be safely called from kvm_create_vm().

Opportunstically drop the #ifdef, KVM provides stubs for
kvm_coalesced_mmio_{init,free}() when CONFIG_KVM_MMIO=n (s390).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220816053937.2477106-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>