This partly reverts ca32373c95 which lets
profiles that suppress packages to alter the package selection for all
devices of the target when building with CONFIG_TARGET_PER_DEVICE_ROOTFS.
In particular, this caused the brcm47xx Edimax PS-1208MFG profile to
disable mtd, dropbear, firewall and other essential packages for all
brcm47xx/generic builds.
To solve this problem, prevent profiles from mangling the global
DEFAULT_PACKAGES selection and restrict the supression of negated
packages to the local PACKAGE variable list only.
Fixes ca32373c95 ("target.mk: let profile remove from DEFAULT_PACKAGES")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>