Create sysfs_dm label.

Prior to this CL, /sys/devices/virtual/block/dm-X was using the generic
sysfs label. This CL creates sysfs_dm label and grants the following
accesses:
 - update_verifier to read sysfs_dm dir and file at
   /sys/devices/virtual/block/dm-X.
 - vold to write sysfs_dm.

Bug: 63440407
Test: update_verifier successfully triggers blocks verification and
      marks a sucessful boot;
Test: No sysfs_dm related denials on sailfish.
Change-Id: I6349412707800f1bd3a2fb94d4fe505558400c95
diff --git a/private/genfs_contexts b/private/genfs_contexts
index 6a95ffb..563da5d 100644
--- a/private/genfs_contexts
+++ b/private/genfs_contexts
@@ -62,6 +62,7 @@
 genfscon sysfs /devices/system/cpu u:object_r:sysfs_devices_system_cpu:s0
 genfscon sysfs /class/leds                        u:object_r:sysfs_leds:s0
 genfscon sysfs /devices/platform/nfc-power/nfc_power u:object_r:sysfs_nfc_power_writable:s0
+genfscon sysfs /devices/virtual/block/dm-       u:object_r:sysfs_dm:s0
 genfscon sysfs /devices/virtual/block/zram0     u:object_r:sysfs_zram:s0
 genfscon sysfs /devices/virtual/block/zram1     u:object_r:sysfs_zram:s0
 genfscon sysfs /devices/virtual/block/zram0/uevent    u:object_r:sysfs_zram_uevent:s0