thermal: Consolidate launching glmark2 as GPU heater

Currently the glmark2 is used to heat GPU for thermal test, this patch
consolidates launching glmark2 from serial console. The glmark2 heater is
optional now, which means no apparent fail will be reported if there is no
glmark2 or it cannot be launched.

Signed-off-by: Hongbo Zhang <hongbo.zhang@linaro.com>
3 files changed