mfd: exynos-lpass: Use common soc/exynos-regs-pmu.h header

The MFD-specific header will go away because it duplicates defines from
exynos-regs-pmu.h.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>