<sys/io.h> is non-standard and even unavailable on some Linux
systems, like arm64. Drop it as it's unused anyway.

<endian.h> is Linux-specific, so don't include it directly, but
let "compiler.h" figure out, whether it should be included.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>