In the #else path ENOSYS is used, however linux/errno.h is not included.
If errno.h has not been included already the compiler errors out even
if the inline function is not referenced.
Make those headers self contained.
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com> Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com> Reviewed-by: Tom Rini <trini@konsulko.com>