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 35d3633083d4c20898d2082241ed3345c9f58baa.

Revert "Revert "projects/imx6/linux: reenable CONFIG_ARM_IMX6_CPUFREQ and CONFIG_REGULATOR_ANATOP support again""
This reverts commit 9243c54226152fa977469adbfbb681797da716d1.

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

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