unix: Add FADV_* constants for linux/arm

This is a followup commit for 9eef40ad
and adds the constants needed for fadvise() on Linux for ARM that were
missing.

Fixes golang/go#16816

Change-Id: Ib7409f48bc07511d7014cb5791a6cc117a9a471e
Reviewed-on: https://go-review.googlesource.com/31641Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/ztypes_linux_arm.go

 // +build arm,linux
 // Created by cgo -godefs - DO NOT EDIT
-// cgo -godefs types_linux.go
+// cgo -godefs types_linux.go | go run mkpost.go
 
 package unix
 
@@ -155,6 +155,15 @@ type Flock_t struct {
 	Pad_cgo_1 [4]byte
 }
 
+const (
+	FADV_NORMAL     = 0x0
+	FADV_RANDOM     = 0x1
+	FADV_SEQUENTIAL = 0x2
+	FADV_WILLNEED   = 0x3
+	FADV_DONTNEED   = 0x4
+	FADV_NOREUSE    = 0x5
+)
+
 type RawSockaddrInet4 struct {
 	Family uint16
 	Port   uint16