Clean up and clarify the populate_sysroot task dependencies. Target sysroot
packages do need their dependencies installed, as do some target/cross
relationships. We can whitelist the *-initial dependencies as these are
never needed indirectly.
(From OE-Core rev: eeec307917234d97be2674beeadef71599fb1487)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>