MIPS: Alchemy: Don't rely on public mmc header to include interrupt.h

The MIPS Alchemy db1300 dev board depends on interrupt.h. Explicitly
include it instead of relying on the public mmc header host.h.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: <linux-mips@linux-mips.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>