Don't duplicate uapi ioprio constants.

This code is only used in init and vold, so I suspect all the
conditional compilation could be moved into the .bp file instead, but
I'm just trying to clean up duplication today...

Test: treehugger
Change-Id: I97013f5de41e109a0cc377400c396145aed569db
diff --git a/libcutils/iosched_policy.cpp b/libcutils/iosched_policy.cpp
index 012c537..f7c724d 100644
--- a/libcutils/iosched_policy.cpp
+++ b/libcutils/iosched_policy.cpp
@@ -24,8 +24,7 @@
 #include <unistd.h>
 
 #if defined(__ANDROID__)
-#define IOPRIO_WHO_PROCESS (1)
-#define IOPRIO_CLASS_SHIFT (13)
+#include <linux/ioprio.h>
 #include <sys/syscall.h>
 #define __android_unused
 #else