drm/amd: Check whether secure display TA loaded successfully

[Why]
Not all renoir hardware supports secure display.  If the TA is present
but the feature isn't supported it will fail to load or send commands.
This shows ERR messages to the user that make it seems like there is
a problem.

[How]
Check the resp_status of the context to see if there was an error
before trying to send any secure display commands.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/1415


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>