ARM: shmobile: cpuidle: Remove the pointless default driver

The default idle driver uses one state with the WFI instruction.
The default idle routine invokes WFI when no cpuidle driver is present.

The default cpuidle driver is pointless and does not give more than the
default idle routine and moreover it pulls all the mathematics tied with
the cpuidle governor for nothing, hence consuming more energy.

Remove the default driver, the related code and register the driver directly.

[compiled only - no board - no test]

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>