F12 for OSD

Audio & Video submenu adds:
UltiSID: on/off (default on)
SID DC Blocker: on/off (default on, used for DC constant debug only)

Audio & Video submenu adds:
Load Custom Filters: *.FLT (will load custom 1 into left UltiSID, custom 2 into right UltiSID as a complete override: custom, offset, etc selects don't work for UltiSID yet)
[Delete /media/fat/config/C64.f7 if you want to go back to the stock filters in the VHDL]

UltiSID Tweaks (new submenu):
US Octasid Mode: off/on (default off, turning off uses UltiSID config for The Tuneful Eight)
US Pseudostereo: off/on (default off, experimental filter/resonance on L/R channel to simulate stereo/phase effects)
US Sync: resid msbrise/us carry 24 (default resid msbrise/us, which is the bugfix for sync on the opposite oscillator polarity/phase)
US Filter Q: resid/UltiSID (default resid, it matches the mister implementation)
US 6581 FltDist Floor: 0-62/off (default 8, this provide enough filter distortion to make mechanicus sounds like a guitar)
US 6581 FltDist Max: 0000-07FF (default 0180)
US 6581 Filt Gain: C2-100 (default $100 which is 100% as the value used is xxx/256)
US 6581 Mixer DC Offsets: on/off (default on, which allows for undocumented digi effects for $d417/$d418)
US 6581 Osc Offset: 000-7F0 (default, 080 which is what is added directly to the 12-bit oscillator output)
US 6581 DC Offs Scale: 0-63 (default, 32, with the larger this number the louder the digi but may introduce more clicking on filter changes)
US 6581 DC Offs Smooth: yes/no (default yes, to prevent annoying clicking on Venus Rising from SID Chip Club)
US Mahoney Mode: no/yes (default no, this is a cheat mode to allow best possible Mahoney digis)
US Wave Comb Mode: resid/UltiSID (default resid, this is needed for Censor Design digis such as Wonderland 13, XIV)

(*) Note that you may change between UltiSID on/off dynamically to sound compare between stock MiSTer SIDs and UltiSID.
Both UltiSID and MiSTer SIDs are written to in lockstep and the only muxing occurs on the sound outputs and OSC3/ENV3 register reads.

Have at it!
260823bsi
