i386: hvf: Reset IRQ inhibition after moving RIP

i386: hvf: Reset IRQ inhibition after moving RIP

The sequence of instructions exposes an issue:
  sti
  hlt

Interrupts cannot be delivered to hvf after hlt instruction cpu because
HF_INHIBIT_IRQ_MASK is set just before hlt is handled and never reset
after moving instruction pointer beyond hlt.

So, after hvf_vcpu_exec() returns, CPU thread gets locked up forever in
qemu_wait_io_event() (cpu_thread_is_idle() evaluates inhibition
flag and considers the CPU idle if the flag is set).

Cc: Cameron Esfahani <[email protected]>
Signed-off-by: Roman Bolshakov <[email protected]>
Message-Id: <20200328174411[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>