[PATCH] add big endian version of ld_/st_ IO access macros and convert main 8xx code to use it

[Paul Mackerras]

Marcelo Tosatti writes:

> eieio/isync are not required. There's no need to execute redudant
> instructions and occupy kernel space.

Given how long it takes to access I/O devices, I don't believe an
extra instruction or two is going to make a measurable difference.
Feel free to show me measurements proving me wrong, of course... :)

Paul.