Draft: Global enable sdmc card interrupts. Ensure UpCall 6 safe
Detail: Interrupts: Enable Global card interrupts in sdmmc_io to match as in sdio_io.
Clear interrupt semaphore on entering irq task, rather than on exit. (Client task can take a while to complete and can cause further legitimate card interrupts. This ensures none are missed.)
Ensure that the UpCall 6 pollword is guaranteed present. Place task structure in a bit of RMA to ensure it is always present. (Even with this, though, the UpCall 6 pollword was unsafe unless set for guaranteed return by using the routine's address as a pointer).
(Will reliably fail in a routine triggered by the RTSupport task card interrupt loop. Both the pollword as given to UpCall6 and the pollword structure demonstrated unsafe defined on the C stack.)
Admin: