drm/amd/display: use kvmalloc for dc_state (v2)

It's large and doesn't need contiguous memory.  Fixes
allocation failures in some cases.

v2: kvfree the memory.

Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>