add comments explaining why recent changes were made, IRQ flood
detection, etc. bugfix added to respect the IRQ enable state of a
controller when exiting the IDE controller menu. exiting the menu no
longer auto-sets it back to IRQ mode. PCI enumeration now automatically
disables the IRQ mode if the IDE controller is a specific known Intel
Haswell chipset (SATA controller emulating IDE), for reasons explained
in the comments.