dtrace/powerpc: Adjust AFRAMES for fbt and profile

FBT_AFRAMES was skipping over too many frames, while PROFILE_AFRAMES was
skipping over too few. Adjust them empirically.

Approved by: re (cperciva)

(cherry picked from commit 635ecbf47015c259226cb47a3de8fc00c9ed5924)
(cherry picked from commit 1026d170f4f70cdeb63cd05819c5557041e8ea94)