ARM: amba: Move definition of struct amba_id to mod_devicetable.h

The general kernel infrastructure for adding module alises during
module post processing expects the affected device type
identification structures in a common header
<linux/mod_devicetable.h>.

This patch simple moves struct amba_id to the common header, and
adds the appropriate include in <linux/amba/bus.h>.

Signed-off-by: Dave Martin <dave.martin@linaro.org>