genirq/affinity: Use default affinity mask for reserved vectors

The reserved vectors at the beginning and the end of the vector space get
cpu_possible_mask assigned as their affinity mask.

All other non-auto affine interrupts get the default irq affinity mask
assigned. Using cpu_possible_mask breaks that rule.

Treat them like any other interrupt and use irq_default_affinity as target
mask.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>