drm/amdgpu: add upper bound check on user inputs in signal ioctl

drm/amdgpu: add upper bound check on user inputs in signal ioctl

Huge input values in amdgpu_userq_signal_ioctl can lead to a OOM and
could be exploited.

So check these input value against AMDGPU_USERQ_MAX_HANDLES
which is big enough value for genuine use cases and could
potentially avoid OOM.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>