power: smb5: Advertise low battery in Type-C Source mode

In Type-C Source mode, enable the generation of a
"typec-or-rid-detect-change" interrupt whenever battery voltage crosses
a preset threshold value (currently set to 3.6V). Determine whether the
crossing is because the voltage is above or below the threshold, and
return this information via the USB PSY property LOW_POWER.

This property is displayed only when in Type-C Source mode.

Change-Id: Id305c7c454bf6423582a952312428d64121e45fb
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>