ARM: dts: OMAP2+: Update DMTIMER compatibility property

Update the DMTIMER compatibility property to reflect the register level
compatibilty between devices and update the various OMAP/AM timer
bindings with the appropriate compatibility string.

By doing this we can add platform specific data applicable to specific
timer versions to the driver. For example, errata flags can be populated
for the timer versions that are impacted.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>