memory: omap-gpmc: Drop custom PM calls with cpu_pm notifier

We can now switch over to using cpu_pm instead of custom calls and make
the context save and restore functions static.

Let's also move the save and restore functions to avoid adding forward
declarations for them. And get rid of the static data pointer while at it.

Cc: Roger Quadros <rogerq@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20210727101034.32148-2-tony@atomide.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>