m4: fix aclocal warning

Running sh autogen.sh during the installation of QATlib reports the
following warning:

  aclocal: warning: couldn't open directory 'm4': No such file or directory

Fix it by adding an empty file (.gitkeep) to the m4 folder on the QATlib
root directory.  Also update .gitignore.

Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>

Author: gcabiddu

.gitignore

@@ -12,7 +12,7 @@
 /install-sh
 /missing
 /libtool
-/m4
+/m4/*
 /ar-lib
 /compile
 /depcomp