linux-phytec-ti

HACK: clocksource: kconfig: allow to select arm global timer manually

This patch changes definition of ARM_GLOBAL_TIMER so it can be
enabled manually. This is required because ARM Global timer
has some limitations:
 - It is not always-on timer on am437x and it can't be
   used as clocksource device if CPU_IDLE=y
 - It doesn't support CPUfreq now
which can't be resolved properly by using kconfig dependencies
in case of multiplatform build.
For example, ARM_GLOBAL_TIMER can't be selected by default
for TI AM437x SOC, because it expected to support cpuidle
and cpufreq in multiplatform build from one side. From
another side - will cpuidle and cpufreq really work depends
not only from kconfig options, but also from PM driver
which has to be loaded.

LKML version:
 https://patchwork.ozlabs.org/patch/579071/

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>