ksyms: Fixup symbols for powerpc in the kernel, not just modules

Summary:
PowerPC kernels are fully position independent, just like kernel modules.
The same fixups that are done for modules therefore need to be done to the
kernel, else symbol resolution in, e.g., DTrace, cannot resolve the kernel
symbols, so only addresses in the kernel are printed, while kernel module
symbols are printed.

Test Plan:
Run lockstat on powerpc64. Note symbols are resolved for kernel and
modules.

Reviewed By: markj
Differential Revision: https://reviews.freebsd.org/D20316