mmc: core: Restructure and simplify code for mmc sleep|awake

The mmc_card_sleep|awake APIs are not being used since the support is
already properly encapsulated within the suspend sequence. Sleep|awake
command is also specific for eMMC.

We remove the sleep|awake bus_ops, the mmc_card_sleep|awake APIs and
move the code into the mmc specific core instead. This also includes
the mmc ops function, mmc_sleepawake. All releated functions have then
become static and we have got far less code to maintain.

Additionally this patch also simplifies the code from mmc_sleepawake,
since it is only used to put the card to sleep and not awake.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>