cpuidle: remove BM_RLD access from idle entry path

cpuidle: remove BM_RLD access from idle entry path

Port below linux patch into xen to reduce overhead from idle entry path.

commit 31878dd86b7df9a147f5e6cc6e07092b4308782b
Author: Len Brown <len.brown@intel.com>
Date:   Wed Jan 28 18:28:09 2009 -0500

    ACPI: remove BM_RLD access from idle entry path

    It is true that BM_RLD needs to be set to enable
    bus master activity to wake an older chipset (eg PIIX4) from C3.

    This is contrary to the erroneous wording the ACPI 2.0, 3.0
    specifications that suggests that BM_RLD is an indicator
    rather than a control bit.

    ACPI 1.0's correct wording should be restored in ACPI 4.0:
    http://www.acpica.org/bugzilla/show_bug.cgi?id=3D689

    But the kernel should not have to clear BM_RLD
    when entering a non C3-type state just to set
    it again when entering a C3-type C-state.

    We should be able to set BM_RLD at boot time
    and leave it alone -- removing the overhead of
    accessing this IO register from the idle entry path.

    Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Wei Gang <gang.wei@intel.com>