ASoC: kirkwood: Remove ARCH_KIRKWOOD dependency

mach-kirkwood has been removed, now that kirkwood lives in
mach-mvebu. Remove ARCH_KIRKWOOD since ARCH_MVEBU is sufficient.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Mark Brown <broonie@linaro.org>