EventHub: Modify the keyboard layout file name for headset button

The keyboard layout file name was formed based on the name of
tabla sound card on current machine. If it doesn't find such
file, it is going to use Generic keyboard layout where the
key mappings are different, even though the scan code is same.
The sound card name differs across different machine types.
So, generalising the keyboard layout file name will work across
all machine types.

CRs-fixed: 344297
Change-Id: I416b6179f51ac98fe7dfae5268ffb58c243540a4