TF700T: Device specific dock battery support

This change adds the specific dock battery tf700t device implementation.

Patchset 2: Remove whitespaces
Patchset 3: Transformers backwards compatibility
Patchset 4: Fix plugged extra (aosp expect int not boolean)

This change requires http://review.cyanogenmod.org/#/c/31040/

Change-Id: Ieaa51a1a2472ae8bdc2c1bd7e9a40bf0b0303a21
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>