powerpc: Enable LLDB on all powerpc architectures

While LLDB on powerpc and powerpcspe builds as-is, on powerpc64 and
powerpc64le it requires adding a couple of additional source files
to build.

Differential review: https://reviews.freebsd.org/D34043
Approved by: dim, imp, emaste

(cherry picked from commit 0b2d2290fe6d4b07d26a4eb0bceadcd2b9b27fd6)