target/ppc: Introduce mmu6xx_get_physical_address()

target/ppc: Introduce mmu6xx_get_physical_address()

Repurpose get_segment_6xx_tlb() to do the whole address translation
for POWERPC_MMU_SOFT_6xx MMU model by moving the BAT check there and
renaming it to match other similar functions. These are only called
once together so no need to keep these separate functions and
combining them simplifies the caller allowing further restructuring.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>