getGpuDmaBufUsageKb: Report usage in Kilobytes

getGpuDmabufUsageKb currently reports the total size of
dma-bufs attached by the GPU device from
/sys/kernel/dmabuf/buffer/<inode>/size nodes. However these
sysfs nodes report the buffer size in bytes.

Convert the value returned by getGpuDmaBufUsageKb to KB.

Bug: 193403146
Test: Manual
Change-Id: Ie17382794f7e4db34ddadf75488d8f82de435ae0

core/jni/android_os_Debug.cpp

@@ -877,7 +877,7 @@ static jlong android_os_Debug_getGpuDmaBufUsageKb(JNIEnv* env, jobject clazz) {
             continue;
         }
 
-        sizeKb += importer_info->second.size;
+        sizeKb += importer_info->second.size / 1024;
     }
 
     return sizeKb;