drm/amd/display: Add missing DCN21 IP parameter

[why]
IP parameter min_meta_chunk_size_bytes is read for bandwidth
calculations but it was never defined.

[how]
Define min_meta_chunk_size_bytes and initialize value to 256.

Reviewed-by: Laktyushkin Dmytro <[e-mail]>
Acked-by: Solomon Chiu <[e-mail]>
Signed-off-by: Victor Lu <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

···
 	.max_page_table_levels = 4,
 	.pte_chunk_size_kbytes = 2,
 	.meta_chunk_size_kbytes = 2,
+	.min_meta_chunk_size_bytes = 256,
 	.writeback_chunk_size_kbytes = 2,
 	.line_buffer_size_bits = 789504,
 	.is_line_buffer_bpp_fixed = 0,