sreadahead: adding readahead system call into bionic libc

Add bionic libc to support readahead system call.
This is needed to enable sreadahead to work.

Change-Id: I3856e1a3833db82e6cf42fd34af7631bd40cc723
Author: Winson Yung <winson.w.yung@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 46e7b1f..5c1e36e 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -50,6 +50,7 @@
 uid_t   getresuid:getresuid32 ()   209
 gid_t   getresgid:getresgid32 ()   211
 pid_t   gettid()                   224
+ssize_t readahead(int, off64_t, size_t)     225
 int     getgroups:getgroups32(int, gid_t *)    205
 pid_t   getpgid(pid_t)             132
 pid_t   getppid()		   64