ARM: OMAP2+: timer: Remove secure timer for DRA7xx HS devices

Timer 12 on DRA7 SoCs is reserved for secure usage on high-secure (HS)
devices. The timer cannot be used by the kernel on HS devices, but is
available on regular general purpose (GP) devices. This is similar to the
behavior on OMAP3 devices, so extend the logic used in commit ad24bde8
("ARM: OMAP3: Dynamically disable secure timer nodes for secure devices")
to remove the secure timer on DRA7xx SoCs at run-time based on the SoC
device type.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>