drm/i915: use a macro to define MOCS entries

Let's use a macro to make tables smaller and at the same time allow us
to add fields that apply to all entries in future.

v2: rewrap lines to respect 80 chars limit and make it more readable
    (from Chris)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190124000604.18861-5-lucas.demarchi@intel.com