drm/amd/display: Add TB_BORROWED_MAX definition

[Why & How]
For DML2 to decouple it from other DML versions.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Chaitanya Dhere <chaitanya.dhere@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c

@@ -31,6 +31,8 @@
 #include "dml_assert.h"
 
 #define DML2_MAX_FMT_420_BUFFER_WIDTH 4096
+#define TB_BORROWED_MAX 400
+
 // ---------------------------
 //  Declaration Begins
 // ---------------------------