drm/amdkfd: add new flag for uncached GPU mapping

The macro is for memory mapped by GPU as uncached.
Signed-off-by: NEric Huang <jinhuieric.huang@amd.com>
Reviewed-by: NOak Zeng <Oak.Zeng@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

include/uapi/linux/kfd_ioctl.h

@@ -351,6 +351,7 @@ struct kfd_ioctl_acquire_vm_args {
 #define KFD_IOC_ALLOC_MEM_FLAGS_NO_SUBSTITUTE	(1 << 28)
 #define KFD_IOC_ALLOC_MEM_FLAGS_AQL_QUEUE_MEM	(1 << 27)
 #define KFD_IOC_ALLOC_MEM_FLAGS_COHERENT	(1 << 26)
+#define KFD_IOC_ALLOC_MEM_FLAGS_UNCACHED	(1 << 25)
 
 /* Allocate memory for later SVM (shared virtual memory) mapping.
  *