drm/i915/uc: Remove redundant header_offset/size definitions

According to Firmware layout definition, CSS header is located
in front of the firmware blob, so header offset is always 0.
Similarly, size of the CSS header is constant and currently
used version is exactly 128.

While here, move type/status enums up and keep them together.

v2: use sizeof consistently (Daniele), update commit message

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190726184212.1836-1-michal.wajdeczko@intel.com