drm/i915/csr: restructure CSR firmware definition macros

Use uniform prefixes for firmware path, version and size. Unify
alignments. Order macro groups as in the if ladder using them. Add
platform specific max firmware size macros for all platforms for clarity
in the if ladder. Place the max firmware size macros in the platform
specific macro groups.

No functional changes.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180927075311.5076-1-jani.nikula@intel.com