The arm7_9_checksum_memory() and arm7_9_blank_check_memory()
routines are not actually specific to the ARM7 and ARM9 core
generations ... they can work for any core which can run
algorithms using basic ARM (not Thumb) instructions.

Rename them; move the declarations to a more generic site;
likewise move the code (and tidy it a bit in the process).

NOTE:  the blank_check() method falsely returned a success
status (0) on one error path, when the algorithm failed.
Fixed this bug.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>