x86: Fix false positive section mismatch in es7000_32.c
The variable apic_es7000_cluster references the function __cpuinit
wakeup_secondary_cpu_via_mip() from a noninit section. So we've been
warned by the following warning. To avoid possible collision between
init/noninit, its best to mark the variable as __refdata.
We were warned by the following warning:
LD arch/x86/kernel/apic/built-in.o
WARNING: arch/x86/kernel/apic/built-in.o(.data+0x198c): Section
mismatch in reference from the variable apic_es7000_cluster to the
function .cpuinit.text:wakeup_secondary_cpu_via_mip()