[PATCH v2] add selinux support to mdev

[Amadeusz Sławiński]

I'm booting in enforcing mode and init initializes SELinux, later
when mdev is started it needs to create files with correct permissions
for system to work correctly. Following patch allows for easy booting
of SELinux system with mdev as /dev manager.

added in v2 - first try to create node with proper file context, if this
doesn't work because node exists, then set context on existing node as it
may be incorect due to devtmpfs mount or manual creation of nodes.

Amadeusz