ARM: OMAP2+: AM43xx: select ARM TWD timer

Make sure to tell the kernel that AM437x devices have ARM TWD timer.

Signed-off-by: Felipe Balbi <balbi@ti.com>
[grygorii.strashko@ti.com: drop ARM Global timer selection, because
 it's incompatible with PM (cpuidle/cpufreq). So, it's unsafe to enable
 it unconditionally]
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>