intel_adsp: boot_complete must be done PRE_KERNEL_1

Commit 759e07be ("intel_adsp: move memory window setup to
PRE_KERNEL_1") moved memory window setup from EARLY to
PRE_KERNEL_1. Similar change must be done to boot_complete, or
otherwise boot-up sequence will not be completed correctly
on all platforms.

Suggested-by: Anas Nashif <anas.nashif@intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>