drm/i915/dmc: define firmware URL locally

Avoid the dependency on intel_uc_fw.h, and allow removal of xe compat
intel_uc_fw.h. If there needs to be duplication of the URL, at least
have the duplication in a sensible way.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/15935837a0c15f861bb2a688cc53514f47153ef3.1712345787.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>