doc: add mlx5 note for Bluefield build configuration
doc: add mlx5 note for Bluefield build configuration

Fixes: d14e4e976f65 ("config: add Mellanox BlueField armv8 SoC")
Cc: stable@dpdk.org

Signed-off-by: Yongseok Koh <76b37c91816d73ef9cf709e3e83a68f2d162f1e2@mellanox.com>
Acked-by: Shahaf Shuler <59427d49da6f2b944fbf4cb5ee70ef3ac25f744f@mellanox.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk