Make 64-bit AIM trap handlers relocatable by changing all absolute branch
instructions to call through pointers instead. In general, these are set
implicitly through relocation processing. One has to be set explicitly in
machdep.c, however, to fit one handler in the tiny (8 instruction) space
available.

Reviewed by: andreast
Differential revision: D1554
Tested on: UP and SMP G5, Cell, POWER5+