KVM: x86: emulator: update the emulation mode after CR0 write

Update the emulation mode when handling writes to CR0, because
toggling CR0.PE switches between Real and Protected Mode, and toggling
CR0.PG when EFER.LME=1 switches between Long and Protected Mode.

This is likely a benign bug because there is no writeback of state,
other than the RIP increment, and when toggling CR0.PE, the CPU has
to execute code from a very low memory address.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20221025124741.228045-14-mlevitsk@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>