PPC: e500: Fix MMUCSR0 emulation

A  "mtspr SPRMMUCSR0, reg"  always flushed TLB0,
because it passed the SPR number 0x3f4 to the flush routine.
But we want to flush either TLB0 or TBL1 depending on the GPR value.

Signed-off-by: Alex Zuepke <alexander.zuepke@hs-rm.de>
[agraf: change subject line]
Signed-off-by: Alexander Graf <agraf@suse.de>