powerpc/mm: Desintegrate MMU_FTR_PPCAS_ARCH_V2

MMU_FTR_PPCAS_ARCH_V2 is defined in cpu_table.h
as MMU_FTR_TLBIEL | MMU_FTR_16M_PAGE.

MMU_FTR_TLBIEL and MMU_FTR_16M_PAGE are defined in mmu.h

MMU_FTR_PPCAS_ARCH_V2 is used only in mmu.h and it is used only once.

Remove MMU_FTR_PPCAS_ARCH_V2 and use
directly MMU_FTR_TLBIEL | MMU_FTR_16M_PAGE

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/829ae1aed1d2fc6b5fc5818362e573dee5d6ecde.1602489852.git.christophe.leroy@csgroup.eu