Improved SD support
- Enable background operation support (in practice, interrupts were correctly specified in this case, but SDIODriver requires higher HAL device versions before trusting us).
- Set up the GPIO lines controlling the WiFi/Bluetooth module. Previously, these were floating, leading to intermittent responses on the SD bus depending on recent activity. Pad configuration is copied from the Linux device tree, and the pattern of high/low voltages were determined empirically.
Requires RiscOS/BuildSys!47 (merged) and RiscOS/Sources/HWSupport/SD/SDIODriver!6 (merged) in order to build.
Requires Support/CI_Source!16 (merged) in order to pass CI.