doc: replace license text with SPDX tag for nfp
doc: replace license text with SPDX tag for nfp

Signed-off-by: Hemant Agrawal <90d96ef1ecd8ed49b97c7897be950e80824a9c5c@nxp.com>
Acked-by: Alejandro Lucero <1ffca3a1926aae782ae3c39a5b308878ba1e5683@netronome.com>

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