max170xx_battery: add fake temperature support

max170xx_battery: add fake temperature support

BZ: 40875

This patch enables the user space to get fake battery temperature
from fuel gauge driver.This is needed for doing conformence tests
by HW teams.

Usage:
To get fake battery temperature reported:
echo 1 > enable_fake_temp

To get real battery temperature:
echo 0 > enable_fake_temp

Change-Id: Iee154da96ba9cb212cf4b52d09101429d8067520
Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
Reviewed-on: http://android.intel.com:8080/52023
Reviewed-by: Koskinen, Ilkka <ilkka.koskinen@intel.com>
Reviewed-by: Mitra, DebalinaX <debalinax.mitra@intel.com>
Reviewed-by: Jena, TapanX <tapanx.jena@intel.com>
Reviewed-by: Tc, Jenny <jenny.tc@intel.com>
Tested-by: Kallappa Manjanna, MadhukumarX <madhukumarx.kallappa.manjanna@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>