x86, genapic: rename int_delivery_mode, et. al.

int_delivery_mode is supposed to mean 'interrupt delivery mode', but
it's quite a misnomer as 'int' we usually think of as an integer type ...

The standard naming for such attributes is 'irq' - so rename the following
fields and macros:

 int_delivery_mode => irq_delivery_mode
 INT_DELIVERY_MODE => IRQ_DELIVERY_MODE
 int_dest_mode     => irq_dest_mode
 INT_DEST_MODE     => IRQ_DEST_MODE

Signed-off-by: Ingo Molnar <mingo@elte.hu>