[PATCH 4/4][POWERPC] Update default irq servers when boot cpu is removed

The xics code does update the default server information when the boot cpu is 
removed.  This patches recognizes when the boot cpu is being removed and updates 
the appropriate information based on the new 'boot cpu'.

Failure to update this information can causes us to leave irqs pinned to cpus 
that are being removed, especially when removing the boot cpu.  The cpu is 
removed from the kernel, but cpu dlpar remove operations fail since we cannot
return the cpu to the hypervisor.

Signed-off-by: Nathan Fonteno <redacted>
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