Setting the DAC write ahead to 1 sample instead of 6

See merge request !636

fix: 18-bit DACs wouldn't set DAC error bit when in HIQTR

See merge request !634

An IOP will set the DAC error bit if FIFO HIQTR is set for six consecutive cycles, but an off-by-two error prevented the IOP from ever counting that high for 18 bit DACs.  20 Bit DACs and 16 bit DACs were not affected.

Adding mfence ops for userspace

See merge request !632

Defining functions for VIO

See merge request !631

Fixing issue where I canged a loop by one, and messed up the DAC delay

See merge request !630

Adding LPTC timing card temp EPICS chan

See merge request !629

Cherry-pick single-threaded awg RPC server into branch 5.1

See merge request !628

This is apparently as tirpc server is meant to be used.  It has unprotected global
state.

Limited testing shows much improved stability (no crashes) when
running basic tests in diaggui.

Adding new LIGO DAC to the RCG/RTS

See merge request !627

Fixing race condition when two models share a DAC, and one is late, the IOP can miss data and won't report anything went wrong.

Improved sys access to LPTC registers

See merge request !626

Also make slot number a bit flexible, doesn't depend on a magic number
to find the  slot number from the file name.

Protect from null input.  May or not be possible, not sure.

Advanced timing registers exposed to sys file system.  Also accessor functions created in the driver.

Add write support for writeable registers in the sys filesystem.

echo nnn > /sys/kernel/gpstime/lptc/regname

nnn can be decimal 0xhex, 0octal, or 0bbinary.

referecne DCC doc T2000406 for register meanings

Updating fe_simulated_stream to run without a GPS driver loaded.

See merge request !625

 * This will fall-back to a software only interface.

Switch order so that IOP prefers Ligo Timing Card to old TDS system

See merge request !622

An IOP that sees both a LIGO Timing Card and a Contect 16/16, which an indicator of the old TDS system, will now choose the LIGO Timing Card.

Note that there's still no way to run 1PPS with a contec1616 installed,
and now no way to run either 1PPS or TDS with a LIGO timing card installed.