CVE-2026-98785: drm/amd/display: check dc_state_create_copy() for NULL in dm_suspend

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: check dcstatecreatecopy() for NULL in dmsuspend

dcstatecreatecopy() can return NULL on allocation failure. dmsuspend() only conditionally skips dmgpuresettoggleinterrupts() and continues execution, returning success. dmresume() then dereferences the NULL cacheddcstate in linkenccfgcopy() and the following dcstate->streamcount loop, crashing during GPU reset recovery.

Return -ENOMEM immediately if the copy fails, so the caller aborts suspend instead of leaving a NULL cached state for resume.

(cherry picked from commit 84b6d7932fdd2857795a257f9f258562a3cddcab)