pt-irq fixes and improvements

pt-irq fixes and improvements

Tools side:
- don't silently ignore unrecognized PT_IRQ_TYPE_* values
- respect that the interface type contains a union, making the code at
  once no longer depend on the hypervisor ignoring the bus field of the
  PCI portion of the interface structure)

Hypervisor side:
- don't ignore the PCI bus number passed in
- don't store values (gsi, link) calculated from other stored values
- avoid calling xfree() with a spin lock held where easily possible
- have pt_irq_destroy_bind() respect the passed in type
- scope reduction and constification of various variables
- use switch instead of if/else-if chains
- formatting

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Yang Zhang <yang.z.zhang@intel.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>