Currently the boot parameters are tied pretty tightly to the bootaction
functionality, but volume and brightness need to be set on the
bootanimation regardless of whether there's a bootaction or not.
Extract boot parameters into a separate class to make it easier to apply
volume/brightness in a future CL.
Bug: 65462981
Test: Manual test, can succesfully read params on boot.
Change-Id: I32daad64cb8aab39fcd0ca17503218e0605ccd27
(cherry picked from commit f78561e7bbe580d0f0dbca7a615c575973ef6ce4)
