DevelopmentSettings: Hide OEM unlock by default

 * The "OEM unlocking" toogle should not be visible on any
   device running LineageOS, for obvious reasons. Allow it only
   to show up for Google devices, such as Pixel, that set
   ro.oem_unlock_supported=1.

Change-Id: I2b09974fc24e783b985de213b504e964771cbcb7