libsnapshot: add helpers to get the flag value

Add helpers for libsnapshot and snapuserd to access flag
vabc_with_ublk_support.

Bug: 414812023
Test: th

Change-Id: I546b2fb113a892416a784763d8e23800fbb624ca
Signed-off-by: Sandeep Dhavale <dhavale@google.com>
6 files changed