Re-add uaccess tag for /dev/kvm

If --dev-kvm-mode is set to something different then 0666, which we
explicitly support, it makes sense to still apply the uaccess tag to
/dev/kvm. For distros which opt to use the default 0666, this change is
a nop.

This partially reverts commit b8fd3d8220.

src/login/70-uaccess.rules

@@ -47,6 +47,9 @@ SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x014001*", TAG+="uaccess"
 # DRI video devices
 SUBSYSTEM=="drm", KERNEL=="card*", TAG+="uaccess"
 
+# KVM
+SUBSYSTEM=="misc", KERNEL=="kvm", TAG+="uaccess"
+
 # smart-card readers
 ENV{ID_SMARTCARD_READER}=="?*", TAG+="uaccess"