clocksource: arm_arch_timer: move enums and defines to header file

To support the arm_arch_timer via ACPI we need to share defines and enums
between the driver and the ACPI parser code.
So we split out the relevant defines and enums into arm_arch_timer.h.

No functional change.

Signed-off-by: Fu Wei <fu.wei@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>