mmc: cmdq: add platform device reference counting for runtime pm

Access to the registers of CQE HCI wrapped by increment/decrement of pm
core usage counter for the platform device.

Change-Id: I9da4aa7d28dbf8e1d2bf62f6d5fa0875bd5b6064
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>