Fixed assembler constraints for lwbrx and lhbrx
Fixed assembler constraints for lwbrx and lhbrx

The biosemu on bimini had some problems with newer versions of GCC ... I saw
on a couple of websites that for lwbrx and lhbrx, the assembler constraint
"Z" should be used instead of "r". This seems to fix the hang.

agraf/SLOF,mdroth/SLOF,qemu/SLOF,open-power-host-os/slof,k0da/SLOF,stefanberger/SLOF-tpm,qemu/SLOF,leilihh/SLOF,mdroth/SLOF,stefanberger/SLOF-tpm,open-power-host-os/slof,aik/SLOF,dgibson/SLOF,dgibson/SLOF,dgibson/SLOF,aik/SLOF,agraf/SLOF,dgibson/SLOF,leilihh/SLOF,agraf/SLOF,open-power-host-os/slof,leilihh/SLOF,k0da/SLOF,k0da/SLOF,agraf/SLOF,qemu/SLOF,leilihh/SLOF,mdroth/SLOF,aik/SLOF,stefanberger/SLOF-tpm,open-power-host-os/slof,k0da/SLOF,mdroth/SLOF