drm/i915/dmc: Use unversioned path for ADLP

The new DMC release for ADLP (v2.18) in linux-firmware adopted the new
convention of using unversioned filenames, so update the driver code for
that new release. Keep the latest versioned path as fallback so we do
not cause regressions.

Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230123182021.31239-3-gustavo.sousa@intel.com