soc: samsung: pmu: Remove duplicated define for ARM_L2_OPTION register

The register ARM_L2_OPTION (0x2608 in Exynos4 and Exynos5 PMU) was
defined twice.  Both names were used in the Exynos542x code.  Simplify
this.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>