fpga: lib: Add synthesizable AXI4-Stream SV components

Components are connected together with AxiStreamIfc. Some features
include:
  (1) Add bytes to the start of a packet
  (2) Remove bytes from a packet
  (3) Wrappers for some older components
      a.  fifo - buffer but imediately pass a packet
      b.  packet_gate - buffer and hold till end of packet
      c.  width_conv - cross clock domains and change width of axi bus

The AxiStreamIf was moved from PkgAxiStreamBfm to its own file. It can
be used to connect to ports with continuous assignment.
AxiStreamPacketIf must be used procedurally but allows the following
new methods:
  - reached_packet_byte - notify when tdata contains a paritcular byte
  - get_packet_byte/get_packet_field - extract a byte or field from axi
  - put_packet_byte/put_packet_field - overwrite a byte or field onto axi


Original-commit: c3bca6c87700054c96320de119a58f6a688dbd5a

lib/axi4s_sv/Makefile.srcs

@@ -0,0 +1,18 @@
+#
+# Copyright 2020 Ettus Research, A National Instruments Brand
+#
+# SPDX-License-Identifier: LGPL-3.0-or-later
+#
+
+##################################################
+# RFNoC Utility Sources
+##################################################
+AXI4S_SV_SRCS = $(abspath $(addprefix $(BASE_DIR)/../lib/axi4s_sv/, \
+AxiStreamIf.sv \
+axi4s_remove_bytes.sv \
+axi4s_remove_bytes_start.sv \
+axi4s_add_bytes.sv \
+axi4s_fifo.sv \
+axi4s_packet_gate.sv \
+axi4s_width_conv.sv \
+))