hwc: Use dynamic_fps node from /sys/devices/virtual/

- With SELinux, the HAL should write to sysfs nodes from
  "/sys/devices/virtual/graphics" instead of "/sys/class/graphics"
- Change HAL to use that file path.

Change-Id: I867a1f94c8f13afe5bbbcb5a61f93599938210d9
1 file changed