drm/xe: Validate uAPI padding and reserved fields

Padding and reserved fields are declared such that they must be
zeroed, so verify that they're all zero in the respective ioctl
functions.

Derived from original patch by mlankhorst.

v2:
	Removed extensions checks where there were none originally. (José)
	Moved extraneous parentheses to the correct places. (Lucas)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Christopher Snowhill <kode54@gmail.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>