charge_state_v2: add battfake console command
charge_state_v2: add battfake console command

Add battfake console command to charge_state_v2.

BUG=none
BRANCH=samus
TEST=load onto samus and use battfake console command to make
sure it works:

> battfake 100
Reporting fake battery level 100%
> battfake -1
Reporting real battery level

Change-Id: I038db92a4859d460b33b1c7e546bc08d5e21582b
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/256070
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,md5555/ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,fourier49/BIZ_EC,eatbyte/chromium-ec,coreboot/chrome-ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,eatbyte/chromium-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,coreboot/chrome-ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,md5555/ec,md5555/ec