As this image isn't buildable without ptest (the packages won't exist),
depend on the ptest DISTRO_FEATURE to ensure we don't try and build it.
(From OE-Core rev: 0fe856d726c6d9c35533e32e70fbe05ef2b88b17)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>