hwmon: qpnp-current-monitor: Add SMPS current monitoring driver

QPNP PMIC SMPS current monitoring driver provides sysfs interface to
user-space clients for configuring current threshold of the regulator.
It also notifies user-space client whenever load current crosses the
configured threshold limit.

Change-Id: Ic4e7210e262bddd3e1aae6f0ebda35fb54931737
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>