linux-*: enable CONFIG_TMPFS_POSIX_ACL

This is required by some software, e.g. bluez/gnome to set some ACLs on /dev/rfkill (see #904 (closed)). While probably nobody will notice on the downstream kernels (as we don't have any proper software there anyways) it's definitely needed on mainline-ish kernels.

Surprisingly only one kernel has broken by enabling this option (linux-sony-tulip) which I've patched up.