HSD #15013478346: arch: arm: mach-socfpga: config: enable arm clocksource (#81)

commit c596299bced8c507c511339711aaa033853bc7f0 from
https://github.com/altera-opensource/linux-socfpga.git socfpga-6.1.55-lts.

This patch is to fix compilation error. Compilation error is
due to clocksource is not enabled on arm architecture.

Signed-off-by: Swee, Leong Ching <leong.ching.swee@intel.com>
Signed-off-by: Liwei Song <liwei.song@windriver.com>