gpu: vivante: First approximation of user space API

I moved all headers directly or indirectly included by etna_viv into a
new directory under include/uapi. This is still way more (10k lines)
than should be in the API, but at least there is a separation between
internal and API headers now.
gpu: vivante: Removed gc_hal_engine.h

This header that was never included.
gpu: vivante: Removed options that are never inspected

Maybe they used on other platforms or in older versions, but they do
not occur in the current Linux driver.
gpu: vivante: Split options header

The options that are only used internally were moved out of the uapi
header. The options that are used by the uapi headers should be
removed, since every different configuration essentially defines a
different API.