amba: Add Kconfig file

Rather than duplicate the ARM_AMBA Kconfig symbol in both 32-bit and
64-bit ARM architectures, move the common definition to drivers/amba
where dependent drivers will be located.

Signed-off-by: Thierry Reding <treding@nvidia.com>

diff --cc arch/arm/Kconfig
Simple merge

diff --cc arch/arm64/Kconfig
Simple merge

diff --cc drivers/amba/Kconfig
Simple merge