arm64: Add 32bit arm compatible dcache definitions

arm64: Add 32bit arm compatible dcache definitions

We want to be able to reuse device drivers from 32bit code, so let's add
definitions for all the dcache options that 32bit code has.

While at it, fix up the DCACHE_OFF configuration. That was setting the bits
to declare a PTE a PTE and left the MAIR index bit at 0. Drop the useless
bits and make the index explicit.

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