dma: iop-adma: allow building without platform headers

Now that iop3xx and iop13xx are gone, the iop-adma driver no
longer needs to deal with incompatible register layout defined
in machine specific header files.

Move the iop32x specific definitions into drivers/dma/iop-adma.h
and the platform_data into include/linux/platform_data/dma-iop32x.h,
and change the machine code to no longer reference those.

The DMA0_ID/DMA1_ID/AAU_ID macros are required as part of the
platform data interface and still need to be visible, so move
those from one header to the other.

Link: https://lore.kernel.org/r/20190809163334.489360-4-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>