sunxi: move SPL-related definitions to platform-specific include

sunxi: move SPL-related definitions to platform-specific include

The sunxi platform currently doesn't seem to make any use of the
asm/arch-sunxi/spl.h file. This patch moves some declarations from
tools/mksunxiboot.c into it.

This enables us to reuse those definitions when extending the
sunxi board code (boards/sunxi/boards.c).

Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>