System call number 78 corresponds to readlinkat.
Where as 78 is mapped to readlink() in syscall.def for
arm.

With this patch, use sys_readlinkat instead of sys_readlink
and update syscall.def to point syscall number 78 to readlinkat()
instead of readlink()
Signed-off-by: Vijaya Kumar K <vijayak@caviumnetworks.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>