meminfo: Add memtrack dmabufinfo library

This is the userspace component for the improved shared memory buffer
tracking.

A new static library called libdmabufinfo will provide APIs to parse dmabuf
debugfs entries. The library can also map and read the file descriptors
per process to cross-reference the global data per process.

This change only adds a global API to read dmabuf stats from debugfs.

Bug: 63860998
Test: dmabufinfo_test
Change-Id: Ib0deedc73337a70875e03e07d3e9a692c4c33e63
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Erick Reyes <erickreyes@google.com>
Signed-off-by: Sandeep Patil <sspatil@google.com>