drm/amdgpu: extend MAX_KIQ_REG_TRY to 1000

Extend retry times of KIQ to avoid starvation situation caused by
long time full access of GPU by other VFs.

Signed-off-by: Jiawei Gu <Jiawei.Gu@amd.com>
Reviewed-by: Emily.Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>