erosq: Rework pluginlib mappings a little
prev/next -> PLA_LEFT/RIGHT
volup/dn -> PLA_UP/DN
scrollwheel -> PLA_SCROLL_*
This will fix bubbles and any other plugin that is explicitly expecting
PLA_SCROLL_* events.
Change-Id: I9fd4c2e6bdd13e147b20e0f0f600e7e0b9a82842