init: early_mount: removing hard-coded paths

Current early mount has some hard-coded paths that are not easy to extend
when we switch verified boot to AVB (external/avb/libavb). This CL uses some
C++ containers to replace those fixed paths.

Bug: 33254008
Test: early mount /vendor with dm-verity on sailfish
Test: early mount /vendor without dm-verity on sailfish
Test: early mount /vendor with dm-verity on bullhead

Change-Id: I32a22fe486d7649e33bb23c9018ddc0428df6069