spi: lantiq: Add support to acknowledge interrupt

On newer chipsets interrupt need to be acknowledged as they use
different interrupt controller which does not acknowledge the
interrupts automatically.

Signed-off-by: Dilip Kota <eswara.kota@linux.intel.com>
Link: https://lore.kernel.org/r/608923b484d9ef239b44bb545c0b79b27030a6ae.1594957019.git.eswara.kota@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>