Move io_* syscalls decoding to a separate file

* desc.c (sys_io_setup, sys_io_destroy, sys_io_submit, sys_io_cancel,
sys_io_getevents, declarations from libaio.h): Move to ...
* aio.c: new file.
* Makefile.am (strace_SOURCES): Add aio.c.
diff --git a/Makefile.am b/Makefile.am
index 9187fa0..c98d8b9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -15,6 +15,7 @@
 AM_CPPFLAGS = -I$(srcdir)/$(OS)/$(ARCH) -I$(srcdir)/$(OS) -I$(builddir)/$(OS)
 
 strace_SOURCES =	\
+	aio.c		\
 	bjm.c		\
 	block.c		\
 	count.c		\