mmc: omap_hsmmc: context save and restore for DT

We want to get rid of the omap specific platform init code
callbacks as they don't play nice with device tree.

Convert the context loss check to be based on a
register state detection instead.

Cc: Andreas Fenkart <afenkart@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
[add check for CON and HCTL in context save and restore function]
Signed-off-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>