Rename usb_charging.c to extpower_usb.c and move to common/

This more clearly indicates what it does - it manages external power
supplied by USB.  This code will be common to multiple boards which
take power via USB, so it might as well move now.

No code changes, just moving the file.

BUG=chrome-os-partner:18343
BRANCH=none
TEST=build spring

Change-Id: Iae74122db38666bc346104a5096fa82df8cb0c19
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/47656
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

board/spring/board.h

@@ -27,6 +27,7 @@
 #define CONFIG_BOARD_PRE_INIT
 #define CONFIG_CHIPSET_GAIA
 #define CONFIG_CMD_PMU
+#define CONFIG_EXTPOWER_USB
 #define CONFIG_HOST_COMMAND_STATUS
 #define CONFIG_I2C
 #define CONFIG_I2C_PASSTHROUGH

board/spring/build.mk

@@ -1,4 +1,4 @@
-# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
+# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
@@ -8,4 +8,4 @@
 CHIP:=stm32
 CHIP_VARIANT:=stm32f100
 
-board-y=board.o usb_charging.o
+board-y=board.o

common/build.mk

@@ -18,6 +18,7 @@ common-$(CONFIG_PMU_TPS65090)+=pmu_tps65090.o pmu_tps65090_charger.o
 common-$(CONFIG_EOPTION)+=eoption.o
 common-$(CONFIG_EXTPOWER_GPIO)+=extpower_gpio.o
 common-$(CONFIG_EXTPOWER_SNOW)+=extpower_snow.o
+common-$(CONFIG_EXTPOWER_USB)+=extpower_usb.o
 common-$(CONFIG_FLASH)+=flash_common.o fmap.o
 common-$(CONFIG_I2C)+=i2c_commands.o
 common-$(CONFIG_I2C_ARBITRATION)+=i2c_arbitration.o