PPC: Fix up e500 cache size setting

When initializing the e500 code, we need to expose its
cache line size for user and system mode, while the mmu
details are only interesting for system emulation.

Split the 2 switch statements apart, allowing us to #ifdef
out the mmu parts for user mode emulation while keeping all
cache information consistent.

Signed-off-by: Alexander Graf <agraf@suse.de>
