base: genlock: Add new functions to get the fd

Add new API to get the file descriptor reference to a lock suitable for
sharing with other processes.

Change-Id: I1b61f44b6d5745a628eb98dfdc876767c46552ea
Signed-off-by: Alex Wong <waiw@codeaurora.org>
genlock: Taking a reference for lock file.
	 This is required as now we have two file descriptor
	 pointing to same file. If one FD is closed, lock file
	 will be closed. Taking this reference will make sure
	 that file doesn't get close. This refrence will go
	 when client will call close on this FD.