init: Create logical partitions via liblp.

Currently, init can create logical partitions by hardcoding them in
fs_mgr or by specifying them in device-tree. This change allows init to
also create logical partitions by using liblp, which stores partition
tables in a physical partition. The current name for this partition is
"android".

Two aspects of this code will change long-term. One, the prototype code
using device-tree will be deleted once fastboot supports logical
partitions. Two, libdm will obsolete most of the code in
fs_mgr_dm_linear.cpp. For now however we preserve how the prototype code
functions and we layer liblp on top of the existing dm_linear logic.

Bug: 79173901
Test: N/A
Change-Id: If014a109da78fa12269bf0df0dda39028ac2d1aa