drm/amd/display: Move vmalloc include to header file

[Why & How]
Move vmalloc.h include code to header file.

Reviewed-by: ChiaHsuan Chung <chiahsuan.chung@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@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/dml21/dml21_wrapper.c

@@ -2,8 +2,6 @@
 //
 // Copyright 2024 Advanced Micro Devices, Inc.
 
-#include <linux/vmalloc.h>
-
 #include "dml2_internal_types.h"
 #include "dml_top.h"
 #include "dml2_core_dcn4_calcs.h"

drivers/gpu/drm/amd/display/dc/dml2/dml2_wrapper.c

@@ -24,8 +24,6 @@
  *
  */
 
-#include <linux/vmalloc.h>
-
 #include "display_mode_core.h"
 #include "dml2_internal_types.h"
 #include "dml2_utils.h"

drivers/gpu/drm/amd/display/dc/os_types.h

@@ -31,6 +31,7 @@
 #include <linux/kgdb.h>
 #include <linux/delay.h>
 #include <linux/mm.h>
+#include <linux/vmalloc.h>
 
 #include <asm/byteorder.h>