ARM: OMAP2+: Simplify system timers definitions

There is a lot of redundancy in the definitions for the various system
timers for OMAP2+ devices. For example, the omap3_am33xx_gptimer_timer_init()
function is the same as the omap3_gp_gptimer_timer_init() function and the
function omap4_sync32k_timer_init() can be re-used for OMAP5 devices.
Therefore, consolidate the definitions to simplify the code.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>