ASoC: wcd: Add key code mapping of buttons

Change the key code mapping of buttons as below
 according to Android L spec.
Button0 0-70 ohm - hook key
Button1 110-180 ohm - voice assist
Button2 210-290 ohm - volume up
Button3 360-680 ohm - volume down

CRs-Fixed: 957863
Change-Id: Ic94b21ad97e9eb183df42b379fa6040fcd16a657
Signed-off-by: Pavan Chikkala <pavanc@codeaurora.org>