powerpc/85xx:Fix MSR[DE] bit in MSR to support debugger

Debugging of e500 and e500v1 processer requires MSR[DE] bit to be set always.
Where MSR = Machine State register

Make sure of MSR[DE] bit is set uniformaly across the different execution
address space i.e. AS0 and AS1.

Signed-off-by: Radu Lazarescu <radu.lazarescu@freescale.com>
Signed-off-by: Catalin Udma <catalin.udma@freescale.com>
Signed-off-by: Marius Grigoras <marius.grigoras@freescale.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>