arm64: defconfig: Ensure CRYPTO_CHACHA20_NEON is selected

Since commit 17ec3e71 ("crypto: lib/Kconfig - Hide arch options from
user"), the CRYPTO_CHACHA20_NEON option is no longer selected by default
due to changes in how crypto library options are exposed and selected.

To restore the previous behavior and ensure CRYPTO_CHACHA20_NEON is
enabled, explicitly select CONFIG_CRYPTO_CHACHA20 in the defconfig. This
pulls in CRYPTO_LIB_CHACHA_INTERNAL and allows CRYPTO_CHACHA20_NEON to be
selected automatically as before.

Fixes: 17ec3e71 ("crypto: lib/Kconfig - Hide arch options from user")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>