Support sparse irq numbering


Linux Kernel Configuration for x86
└─>Processor type and features
└─>Support sparse irq numbering
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
This enables support for sparse irqs. This is useful for distro
kernels that want to define a high CONFIG_NR_CPUS value but still
want to have low kernel memory footprint on smaller machines.

( Sparse IRQs can also be beneficial on NUMA boxes, as they spread
out the irq_desc[] array in a more NUMA-friendly way. )

If you don't know what to do here, say N.