Add rtdm_irq_request_affine and rtdm_irq_set_affinity to start IRQs or
specific CPUs or move them around. So far, this was unsupported and made
users bypass layer to configure the desired affinity. Starting with the
right affinity also avoids hitting the wrong CPU at least once before
the IRQ can be live-migrated.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>