First cut of PowerPC(64) bsd-user
Fix the syscall frame layout to match FreeBSD
Set the correct TLS address
Set ELF caps like in Linux
Fix signal and context handling
Set up the argument registers for the process correctly.
PowerPC uses aligned register pairs, too
Move the user stack down a bit, to avoid an assertion failure.
Adjust the stack frame down by two, to hold the frame pointer and return address.