Commit de88cbb7 moved definitions of chained_irq_enter and
chained_irq_exit to a generic header, which must be now included instead
of the legacy arch-specific one.

This patch fixes build error caused by including the legacy header
leading to undefined chained_irq_enter and chained_irq_exit symbols.
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>