libpam: split /etc/environment into pam-plugin-env package

libpam: split /etc/environment into pam-plugin-env package

Since systemd-v255, pam-plugin-umask is pulled in by by the logind
package config for systemd. This causes /etc/environment to be installed
as part of libpam-runtime. In our case, this broke do_rootfs for our
image, because /etc/environment is already provided by another (custom)
recipe.

Fix this by making the /etc/environment file part of the pam-plugin-env
package, which isn't automatically pulled in by systemd-logind. It also
happens to be the where it should be, as the file is installed as part
of the pam_env plugin.

Signed-off-by: Martin Hundebøll <martin@geanix.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>