libcutils: make vendor_ramdisk_available. am: 55015ffb82 am: 861fd6376b am: 9485558332 am: 304ae82046

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1477501

Change-Id: I3c7e80aa56ee9d406e7650ea809a97cad97b3f09