x86: fix dom0 S3 when x2apic is used.

x86: fix dom0 S3 when x2apic is used.

1) Some variables and functions in xen/arch/x86/genapic/x2apic.c
should not be marked with __init* as they will be used during s3
resume;
2) In do_suspend_lowlevel -> restore_rest_processor_state ->
mcheck_init, lapic is accessed, but x2apic hasn't been re-enabled yet
(x2apic is re-enabled() in device_power_up -> lapic_resume). The patch
moves mcheck_init to a later place.

Signed-off-by: Dexuan Cui <dexuan.cui@intel.com>