Declare all extern blocks as `extern "C"`

src/psp/atrac.rs

src/psp/codec.rs

src/psp/hprm.rs

src/psp/jpeg.rs

src/psp/mp3.rs

src/psp/nand.rs

src/psp/openpsid.rs

src/psp/registry.rs

src/psp/sircs.rs

src/psp/umd.rs

src/psp/usb.rs

src/psp/wlan.rs