drm/amdgpu/psp: Enlarge PSP TMR SIZE from 3M to 4M.

Enlarge the PSP TMR SIZE to 4M for dual UVD fw front-door loading.

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>