In preparation for turning the decompressor's cache clean/flush
operations into proper by-VA maintenance for v7 cores, pass the
start and end addresses of the regions that need cache maintenance
into cache_clean_flush in registers r0 and r1.

Currently, all implementations of cache_clean_flush ignore these
values, so no functional change is expected as a result of this
patch.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>