fstrim: prep for supporting a deep trim ioctl

This adds an "fstrim dodtrim" command which will attempt to use
the FIDTRIM ioctl() if FIDTRIM is defined in the uapi/linux/fs.h.
If not, it will fail with EINVAL.

If no FIDTRIM is defined, it does not affect the "fstrim dotrim".

Change-Id: Icbfd621abb592b170db06f749e5eedfd1175f723
diff --git a/fstrim.h b/fstrim.h
index e46e804..185d998 100644
--- a/fstrim.h
+++ b/fstrim.h
@@ -17,7 +17,7 @@
 #ifdef __cplusplus
 extern "C" {
 #endif
-    int fstrim_filesystems(void);
+    int fstrim_filesystems(int deep_trim);
 #ifdef __cplusplus
 }
 #endif