drm/amd/display: Fix white screen page fault for gpuvm

[Why]
The "base_addr_is_mc_addr" field was added for dcn3.1 support but
pa_config was never updated to set it to false.

Uninitialized memory causes it to be set to true which results in
address mistranslation and white screen.

[How]
Use memset to ensure all fields are initialized to 0 by default.

Fixes: 64b1d0e8

 ("drm/amd/display: Add DCN3.1 HWSEQ")
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org