mmc: core: Initiate suspend|resume from mmc bus instead of mmc host

The host should be responsible to suspend|resume the host and not the
card. This patch changes this behaviour, by moving the responsiblity
to the mmc bus instead which already holds the card device.

The exported functions mmc_suspend|resume_host are now to be considered
as depcrecated. Once all host drivers moves away from using them, we
can remove them. As of now, a successful error code is always returned.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>