drm/amdkfd: add new flag for svm

It is to add new option for always keeping gpu mapping.
Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

include/uapi/linux/kfd_ioctl.h

@@ -613,6 +613,8 @@ enum kfd_mmio_remap {
 #define KFD_IOCTL_SVM_FLAG_GPU_EXEC    0x00000010
 /* GPUs mostly read, may allow similar optimizations as RO, but writes fault */
 #define KFD_IOCTL_SVM_FLAG_GPU_READ_MOSTLY     0x00000020
+/* Keep GPU memory mapping always valid as if XNACK is disable */
+#define KFD_IOCTL_SVM_FLAG_GPU_ALWAYS_MAPPED   0x00000040
 
 /**
  * kfd_ioctl_svm_op - SVM ioctl operations