Nami: Enable CONFIG_BATTERY_REQUESTS_NIL_WHEN_DEAD

When any of battery cells are near the Cell Under Voltage, battery
enters shutdown mode. However, battery cells can continue to discharge
due to self discharge. Battery cell vendor defines the minimum
acceptable cell voltage. If the cell voltage falls below that value,
battery BMS does not close the C-FET and the battery is considered
permanently dead.

So, every time battery enters shutdown mode, the BMS executes SUV
status check to see whether cells are in safe range to charge.

Gauge IC turns on C-fet after a 5 sec delay. During this delay, the
gauge requests 0mA charging current and 0V charging voltage.

During SUV check, battery gauge monitors the external voltage by the
charger through "battery present through" setting.
If the external voltage is less than the threshold, the BMS goes to
shutdown mode again and this repeats.

This patch enables CONFIG_BATTERY_REQUESTS_NIL_WHEN_DEAD so that the
EC will supply voltage & current even if the battery requests 0V, 0A
at 0% soc, which only happens when the BMS is exiting shutdown mode.

Battery gauge IC: TI BQ40Z50
Battery gauge FW version: 1.06 for BYD/ 1.07 for LG and Simplo.

BUG=b:73921750
BRANCH=none
TEST=Check dead battery can be charged battery to normal mode.

Change-Id: Ib7e12a0596d53377c58eb17c980cd7e01576de7c
Signed-off-by: raymondchou <raymond_chou@compal.corp-partner.google.com>
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/910608
Commit-Ready: Raymond Chou <raymond_chou@compal.corp-partner.google.com>

board/nami/board.h

@@ -82,6 +82,7 @@
 #define CONFIG_BATTERY_DEVICE_CHEMISTRY "LION"
 #define CONFIG_BATTERY_SMART
 #define CONFIG_PWR_STATE_DISCHARGE_FULL
+#define CONFIG_BATTERY_REQUESTS_NIL_WHEN_DEAD
 
 /* Charger */
 #define CONFIG_CHARGE_MANAGER