crypto: marvell - CRYPTO_DEV_OCTEONTX2_CPT should depend on ARCH_THUNDER2

The Marvell OcteonTX2 CPT physical function PCI device is present only
on OcteonTx2 SoC, and not available as an independent PCIe endpoint.
Hence add a dependency on ARCH_THUNDER2, to prevent asking the user
about this driver when configuring a kernel without OcteonTx2 platform
support.

Fixes: 5e8ce833 ("crypto: marvell - add Marvell OcteonTX2 CPT PF driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>