nvme-tcp: fix link failure for TCP auth

The nvme fabric driver calls the nvme_tls_key_lookup() function from
nvmf_parse_key() when the keyring is enabled, but this is broken in a
configuration with CONFIG_NVME_FABRICS=y and CONFIG_NVME_TCP=m because
this leads to the function definition being in a loadable module:

x86_64-linux-ld: vmlinux.o: in function `nvmf_parse_key':
fabrics.c:(.text+0xb1bdec): undefined reference to `nvme_tls_key_lookup'

Move the 'select' up to CONFIG_NVME_FABRICS itself to force this
part to be built-in as well if needed.

Fixes: 5bc46b49 ("nvme-tcp: check for invalidated or revoked key")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>