macsec: fix crypto Kconfig dependency

The new MACsec driver uses the AES crypto algorithm, but can be configured
even if CONFIG_CRYPTO is disabled, leading to a build error:

warning: (MAC80211 && MACSEC) selects CRYPTO_GCM which has unmet direct dependencies (CRYPTO)
warning: (BT && CEPH_LIB && INET && MAC802154 && MAC80211 && BLK_DEV_RBD && MACSEC && AIRO_CS && LIBIPW && HOSTAP && USB_WUSB && RTLLIB_CRYPTO_CCMP && FS_ENCRYPTION && EXT4_ENCRYPTION && CEPH_FS && BIG_KEYS && ENCRYPTED_KEYS) selects CRYPTO_AES which has unmet direct dependencies (CRYPTO)
crypto/built-in.o: In function `gcm_enc_copy_hash':
aes_generic.c:(.text+0x2b8): undefined reference to `crypto_xor'
aes_generic.c:(.text+0x2dc): undefined reference to `scatterwalk_map_and_copy'

This adds an explicit 'select CRYPTO' statement the way that other
drivers handle it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: c09440f7 ("macsec: introduce IEEE 802.1AE driver")
Signed-off-by: David S. Miller <davem@davemloft.net>