Move mount parser to a separate file

* mount.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* system.c: Move sys_mount and related code to mount.c.
diff --git a/Makefile.am b/Makefile.am
index e6dff3e..4daa7c7 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -37,6 +37,7 @@
 	ldt.c		\
 	loop.c		\
 	mem.c		\
+	mount.c		\
 	mtd.c		\
 	net.c		\
 	or1k_atomic.c	\