add REQUIRED to platform field
add REQUIRED to platform field

Signed-off-by: zhouhao <f577ade201aa03d612c19915a089dc6084d45cd9@cn.fujitsu.com>

hqhq/specs,wking/opencontainer-specs,wking/opencontainer-runtime-spec,hqhq/runtime-spec,opencontainers/runtime-spec,opencontainers/specs,laijs/specs