target-ppc: mmu_ctx_t should not be a global type

target-ppc: mmu_ctx_t should not be a global type

mmu_ctx_t is currently defined in cpu.h.  However it is used for temporary
information relating to mmu translation, and is only used in mmu_helper.c
and (now) mmu-hash{32,64}.c.  Furthermore it contains information which
should be specific to particular MMU types.  Therefore, move its definition
to mmu_helper.c.  mmu-hash{32,64}.c are converted to use new data types
private to the relevant MMUs (identical to mmu_ctx_t for now, but that will
change in future patches).

Signed-off-by: David Gibson <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>