Hard-reset back to launcher/sysmenu on exit when bootstub isn't present, add some I2C device registers to i2c.h. Shutdown DSi-only hw in arm7 systemShutDown. Add missing bit to the combined arm7 I2C PWRCNT bitmask in the I2C IRQ. This only hard-resets when arm7 exits, arm9 exiting will cause shutdown. Some FIFO code for I2C needs implemented for that.