KVM: x86: WARN and reject KVM_RUN if vCPU's MP_STATE is SIPI_RECEIVED

KVM: x86: WARN and reject KVM_RUN if vCPU's MP_STATE is SIPI_RECEIVED

WARN if KVM_RUN is reached with a vCPU's mp_state set to SIPI_RECEIVED, as
KVM no longer uses SIPI_RECEIVED internally, and should morph SIPI_RECEIVED
into INIT_RECEIVED with a pending SIPI if userspace forces SIPI_RECEIVED.

See commit 66450a21f996 ("KVM: x86: Rework INIT and SIPI handling") for
more history and details.

Link: https://lore.kernel.org/r/20250605195018.539901-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>