mmc: core: disable runtime-pm if MMC_CAP2_CORE_RUNTIME_PM is not defined

There is currently no mechanism to disable the runtime-pm
of eMMC/SD card. This patch adds the mechanism to disable
runtime-pm of eMMC/SD if MMC_CAP2_CORE_RUNTIME_PM is not
defined.

It sets the platform, class and card device as RPM_ACTIVE
irrespective of the capability but doesn't enable it.
The card is never runtime-suspended and hence the
corresponding mmc_host and platform device are not
runtime-suspended as well.

A capability MMC_CAP2_CORE_PM is used to select the use
of core power-management framework.

CRs-Fixed: 490021
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Change-Id: I394a81a889ab7d4f0f0e6fe4b932630e30fc16c9