drm/i915/dmc: use kernel types

Change all fields in intel_package_header and intel_dmc_header whose
meaning are 1-byte numbers to use u8.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190607091230.1489-2-lucas.demarchi@intel.com