MFC: r190112

• As suggested by OpenSolaris use up-burst-sizes for determining the supported burst sizes.
• Add support for 64-bit burst sizes (required for SBus GEM).
• Register our interrupt filters with the revived INTR_FAST so they these interrupts can even interrupt filters of device drivers as necessary.
• Failing to register as interrupt controller during attach shouldn't be fatal so just inform about this instead of panicing.
• Take advantage of KOBJMETHOD_END.
• Remove some redundant variables.
• Add missing const.