drm/radeon/dpm: fix compilation with certain versions of gcc

Add #include <linux/seq_file.h> to *_dpm.c files

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/ni_dpm.c b/drivers/gpu/drm/radeon/ni_dpm.c
index 8497ca6..a4cb99c 100644
--- a/drivers/gpu/drm/radeon/ni_dpm.c
+++ b/drivers/gpu/drm/radeon/ni_dpm.c
@@ -28,6 +28,7 @@
 #include "ni_dpm.h"
 #include "atom.h"
 #include <linux/math64.h>
+#include <linux/seq_file.h>
 
 #define MC_CG_ARB_FREQ_F0           0x0a
 #define MC_CG_ARB_FREQ_F1           0x0b