selftests/android/ion: Makefile: fix build error

Fails to build iomap_test.c due to missing include

gcc  -I. -I../../../../../drivers/staging/android/uapi/ -Wall -O2 -g
ionmap_test.c ipcsocket.c ionutils.c   -o ionmap_test
ionmap_test.c:12:27: fatal error: linux/dma-buf.h: No such file or
directory
 #include <linux/dma-buf.h>
                           ^
compilation terminated.
<builtin>: recipe for target 'ionmap_test' failed
make[2]: *** [ionmap_test] Error 1

In the current code, we add a new -I ../../../../../usr/include/ to the
INCLUDEDIR variable. Also add ionmap_test to the .gitignore file.

Fixes: ac93f704 ("selftests: ion: Add simple test with the vgem driver")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>