power: smb5-lib: Set default WLS VOUT to 5 V when standalone

In the absence of secondary chargers, set the VOUT of the wireless
charger to 5V upon DC attach by default.

Change-Id: Idb11260567446f4feb49c121a17969cfe09b3829
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>