anv: Rework the internal BO allocation API

anv: Rework the internal BO allocation API

This makes a number of changes to the current API:

 1. Everything is renamed to anv_device_* instead of anv_bo_cache_*
    because the BO cache is soon going to be the sole BO allocation path
    and not some special case to make import/export work.

 2. Drop the cache parameter.  It's totally redundant with the device
    and just annoying to keep typing.

 3. Rework flags so that they go the convenient direction for usage in
    ANV rather than whichever awkward way the i915 specified it to
    maintain backwards compatibility.  This also gives us the
    opportunity to set some defaults.

 4. Add flags for mapping and coherency.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>