ARM: OMAP: Add support for dmtimer v2 ip

The registers are slightly different between v1 and v2 ip that
is available in omap4 and later for some timers.

Add support for v2 ip by mapping the interrupt related registers
separately and adding func_base for the functional registers.

Also disable dmtimer driver features on omap4 for now as
those need the hwmod conversion series to deal with enabling
the timers properly in omap_dm_timer_init.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Tested-by: Hemant Pedanekar <hemantp@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>