arm64: cpuidle: remove generic cpuidle support

The arm64 support of the generic ARM cpuidle driver was removed. This
let us remove all support code for it.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20220529181329.2345722-3-michael@walle.cc


Signed-off-by: Will Deacon <will@kernel.org>