bitbake: add readlink to HOSTTOOLS

If systemd has EFI enabled it uses readlink.

(From OE-Core rev: ace3c0fff40604450ea8f0a669aaa37fbe730069)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/conf/bitbake.conf

@@ -494,7 +494,7 @@ HOSTTOOLS += " \
     fgrep file find flock g++ gawk gcc getconf getopt git grep gunzip gzip \
     head hostname id install ld ldd ln ls make makeinfo md5sum mkdir mknod \
     mktemp mv nm objcopy objdump od patch perl pod2man pr printf pwd python2 \
-    python2.7 python3 ranlib readelf readlink rm rmdir rpcgen sed seq sh sha256sum \
+    python2.7 python3 ranlib readelf readlink realpath rm rmdir rpcgen sed seq sh sha256sum \
     sleep sort split stat strings strip tail tar tee test touch tr true uname \
     uniq wc wget which xargs \
 "