2370eba9f5
[Why] When some tools performing psp mailbox attack, the readback value of register can be a random value which may break psp. [How] Use a psp wptr cache machanism to aovid the change made by attack. v2: unify change and add detailed reason Signed-off-by: Victor Zhao <Victor.Zhao@amd.com> Signed-off-by: Jingwen Chen <Jingwen.Chen2@amd.com> Reviewed-by: Monk Liu <monk.liu@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>