Bush Internet TV (IBX100) STB support changes: VCO presence
This MR depends RiscOS/Sources/Kernel!73 (merged) which needs to be merged first!
Some IOMD hardware types (notably Lazarus, the Bush Internet TV aka IBX100 set-top) don't have a VIDC VCO. Historically this was handled by a compile-time directive in the VIDC20 driver, but this has now been cleaned up. With this change, the HAL is responsible for indicating to the VIDC20 driver that the hardware doesn't have a VCO, and for the VIDC20 driver to ignore the VCO as a result.
The default (device dependent flags = 0) is to use the VCO, as we always have on desktops.
The R12 to R10 change in CalculateVCO is because R12 contains the driver workspace pointer, and we need that to access the device descriptor.
The LTORG and ADR -> ADRL changes are to fix an issue which occurred when debugging was enabled: the VIDC20 driver would not assemble because the literal sections were not at the end of their respective functions, and the VSyncHandler had moved too far away from the ADR.