init: Factor GetBlockDeviceInfo() out of GetBlockDeviceSymlinks()

Later code will want to use GetBlockDeviceInfo(), so factor it out to
a helper function. This change is intended to be a no-op.

Bug: 316324155
Test: Build & boot
Change-Id: If5d63f39efcd84a07eb8c6fa4f28bda45c4cbe5c
2 files changed