refactor(allwinner): consolidate sunxi_cfg.h files

refactor(allwinner): consolidate sunxi_cfg.h files

The header files describing the CPU cluster configuration IP block for
the H6 and H616 are actually identical, so merge them into one file and
move that to a common location. There is an upcoming SoC which will
similarly share a header file with the R329 SoC, so move that to the
same location already. In Allwinner's BSP source those two SoC groups
are typically called "NCAT" and "NCAT2", so use those names for the
shared header files. No functional change.

Change-Id: I98318373577344dbe228a81fa331ce660df32b5f
Signed-off-by: Andre Przywara <andre.przywara@arm.com>