In the PCB struct, we need to match the VSX register file layout correctly, as the VSRs shadow the FPRs.
In LE, we need to have a dword of padding before the fprs so they end up on the correct side, as the struct may be manipulated by either the FP routines or the VSX routines.
Additionally, when saving and restoring fprs, we need to explicitly target the fpr union member so it gets offset correctly on LE.
Fixes weirdness with FP registers in VSX-using programs (A fpr that was saved by the FP routines but restored by the VSX routines was becoming 0 due to being loaded to the wrong side of the vsr.)
Original patch by jhibbits.