revert last both reverts, and fix #3628 with enabling CONFIG_REGULATOR_FIXED_VOLTAGE

Revert "Revert "projects/*/linux: disable CONFIG_REGULATOR, this fixes #3617""
This reverts commit 35d36330.

Revert "Revert "projects/imx6/linux: reenable CONFIG_ARM_IMX6_CPUFREQ and CONFIG_REGULATOR_ANATOP support again""
This reverts commit 9243c542

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projects/imx6/linux: enable CONFIG_REGULATOR_FIXED_VOLTAGE, this fixes #3628

Signed-off-by: Stephan Raue <stephan@openelec.tv>