clocksource/drivers/sprd: Fix Kconfig dependency

SPRD arch doesn't select SPRD_TIMER, so this config would not
appear even if ARCH_SPRD is set but COMPILE_TEST not.

Fix the dependency of this config with SPRD arch, and set a
default value for it, also leave other choices for EXPERT.

Signed-off-by: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>