libavb expects to be able to read the maximum vbmeta size, so we must
provide a partition which matches this or the read will fail.
Bug: 181923506
Test: m MicrodroidHostTestCases
libavb tries
Change-Id: Icc5b86ccd98e3ed9c4269e584f35dbfbdf1b0730
The module type is to create vbmeta image out of other partitions.
Bug: 180676957
Test: m microdroid_vbmeta microdroid_vbmeta_system
Inspect the built image using `avbtool info_image --image <image>`
Change-Id: Iac92e9ab1640dcd488af69842e09850a91262bf1