drm_hwcomposer: Move platform-specific importer headers

Now that importer.h is platform.h, move the platform-specific
headers to match.

BUG=b/28117135
TEST=compiles

Change-Id: I08563505b77529257892841845ef4117d2992bb0
Signed-off-by: Sean Paul <seanpaul@chromium.org>
diff --git a/drmgenericimporter.cpp b/drmgenericimporter.cpp
index 24af138..d57db6a 100644
--- a/drmgenericimporter.cpp
+++ b/drmgenericimporter.cpp
@@ -17,8 +17,8 @@
 #define LOG_TAG "hwc-drm-generic-importer"
 
 #include "drmresources.h"
-#include "drmgenericimporter.h"
 #include "platform.h"
+#include "platformdrmgeneric.h"
 
 #include <drm/drm_fourcc.h>
 #include <xf86drm.h>