thunderbolt: Extend NVM version fields to 32-bits

In order to support non-Intel NVM image formats extend the NVM major and
minor version to 32-bits to better accommondate different versioning
schemes.

No functional impact.

Signed-off-by: Szuying Chen <Chloe_Chen@asmedia.com.tw>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>