Android.mk: clean dependencies and clear variables

Dependencies being built with newline files in between
were also including the list of files without the newlines,
thus make would have to process 3n-1 files instead of 2n-1
where n is the number of files to process.

Additionally the *_with_nl variables were not being cleared
out and polluting Make's global name-space.

Change-Id: I76ea1a3dfae994b32991730aea7e4308da52a583
Signed-off-by: William Roberts <william.c.roberts@intel.com>