sdmmc_isr() function

SDMMC interrupt handler All communication in SD protocol is driven by the master, and the hardware handles things like stop commands automatically. So the interrupt handler doesn't need to do much, we just push interrupt status into a queue, clear interrupt flags, and let the task currently doing communication figure out what to do next. This also applies to SDIO interrupts which are generated by the slave. Card detect interrupts pose a small issue though, because if a card is plugged in and out a few times, while there is no task to process the events, event queue can become full and some card detect events may be dropped. We ignore this problem for now, since the there are no other interesting events which can get lost due to this.