data_smart: split expanded removal values when handling _remove

data_smart: split expanded removal values when handling _remove

Given these assignments:

 TEST="a b c d"
 TEST_remove = "b d"

TEST evaluates to "a c".  However, if the _remove override is given as a
variable:

 TEST="a b c d"
 FOO = "b d"
 TEST_remove = "${FOO}

TEST evaluates to "a b c d", because when FOO is expanded it isn't split into a
list.

Solve this by splitting all members of removeactive once they've been expanded.

[ YOCTO #7272 ]

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