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This appends sunxi-meminfo to the TARGET_TOOLS, and adds a new rule
to fix the compilation of sunxi-pio (by making it *cross-compile*
for the target).

Additionally adds a new build target "make install-misc".

For more details, see github issues #69 and #70.
Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>