mmc: core: Signal wakeup event at card insert/removal

We want to give user space provision to fully consume a card
insert/remove event, when the event was caused by a wakeup irq.

By signaling the wakeup event for a time of 5 s for devices configured
as wakeup capable, we likely will be prevent a sleep long enough to let
user space consume the event.

To enable this feature, host drivers must thus configure their devices
as wakeup capable.

This is a reworked implementation of the old wakelocks for the mmc
subsystem, originally authored by Colin Cross and San Mehat for the
Android kernel. Zoran Markovic shall also be given cred for recently
re-trying to upstream this feature.

Cc: San Mehat <san@google.com>
Cc: Colin Cross <ccross@android.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Zoran Markovic <zoran.markovic@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Zoran Markovic <zoran.markovic@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>