Earlgrey: newest tlul_fifo_async doesn't work in Verilator

[rkapuscik]

After updating Opentitan to newest version, tlul_fifo_async.sv is failing with:

%Error: /media/hdd/uhdm/uhdm-integration/verilator/uhdm-integration/../uhdm-tests/opentitan/module_tests//..//opentitan/build/lowrisc_dv_chip_verilator_sim_0.1/src/lowrisc_prim_fifo_0/rtl/prim_fifo_async.sv:255:35: Can't find definition of task/function: 'gray2dec'
%Error: /media/hdd/uhdm/uhdm-integration/verilator/uhdm-integration/../uhdm-tests/opentitan/module_tests//..//opentitan/build/lowrisc_dv_chip_verilator_sim_0.1/src/lowrisc_prim_fifo_0/rtl/prim_fifo_async.sv:257:35: Can't find definition of task/function: 'gray2dec'
%Error: /media/hdd/uhdm/uhdm-integration/verilator/uhdm-integration/../uhdm-tests/opentitan/module_tests//..//opentitan/build/lowrisc_dv_chip_verilator_sim_0.1/src/lowrisc_prim_fifo_0/rtl/prim_fifo_async.sv:259:31: Can't find definition of task/function: 'dec2gray'
%Error: /media/hdd/uhdm/uhdm-integration/verilator/uhdm-integration/../uhdm-tests/opentitan/module_tests//..//opentitan/build/lowrisc_dv_chip_verilator_sim_0.1/src/lowrisc_prim_fifo_0/rtl/prim_fifo_async.sv:260:31: Can't find definition of task/function: 'dec2gray'
%Error: Exiting due to 4 error(s)

Those functions are defined in prim_fifo_async.sv (see #494 first).

[RRozak]

The same problem as in #494, I mark it as blocked