mmc: host: Add support for card detect gpio sharing

On few targets (scuba), the sdcard vdd regulator is shared.
On removal of SD-Card, the MGPI feature will automatically turned off
the card vdd regulator. So, during card removal, it is always advised
to unvote the vdd regulator from all the shared clients.

Always use IRQF_SHARED flag, inorder for the other clients to register
and get card detect/removal events for the same gpio-irq.

Change-Id: Ieebd962287eabd67d2afde50280db45a9fa5c7c6
Signed-off-by: Pradeep P V K <ppvk@codeaurora.org>