loaders: IO: Add GP_IOReadB2

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
build: Update loader symbols.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
loaders: PSD: Work on combined image loading.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>