xen/events: remove some simple helpers from events_base.c

The helper functions type_from_irq() and cpu_from_irq() are just one
line functions used only internally.

Open code them where needed. At the same time modify and rename
get_evtchn_to_irq() to return a struct irq_info instead of the IRQ
number.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Signed-off-by: Juergen Gross <jgross@suse.com>