x86: check_timer cleanup

Impact: make check-timer more robust potentially solve boot fragility

For edge trigger io-apic routing, we already unmasked the pin via
setup_IO_APIC_irq(), so don't unmask it again.

Also call local_irq_disable() between timer_irq_works(), because it
calls local_irq_enable() inside.

Also remove not needed apic version reading for 64-bit

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>