ARM: OMAP: Remove timer function pointer for context loss counter

For OMAP2+ devices, a function pointer that returns the number of times a timer
power domain has lost context is passed to the dmtimer driver. This function
pointer is only populated for OMAP2+ devices and it is pointing to a platform
function. Given that this is a platform function, we can simplify the code by
removing the function pointer and referencing the function directly. We can use
the OMAP_TIMER_ALWON flag to determine if we need to call this function for
OMAP1 and OMAP2+ devices.

The benefit of this change is the we can remove the function pointer from the
platform data and simplifies the dmtimer migration to device-tree.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>