These are similar to the mips24k performance counters - some are
available on perfcnt0/3, some are available on perfcnt1/4.
However, the events aren't all the same.
* Add the events, named the same as from Linux oprofile.
* Verify they're the same as "MIPS32(R) 74KTM Processor Core Family
Software User's Manual"; Document Number: MD00519; Revision 01.05.
* Rename INSTRUCTIONS to something else, so it doesn't clash with
the alias INSTRUCTIONS. I'll try to tidy this up later; there
are a few other aliases to add and shuffle around.
Tested:
* QCA9558 SoC (AP135 board) - MIPS74Kc core (no FPU.)
* make universe; where it didn't fail for other reasons.
TODO:
* It'd be nice to support the four performance counters
in at least this hardware, rather than just two.
Reviewed by: bsdimp ("looks good; don't break world".)
