On imx6sl-evk board the VGEN1 regulator powers up the NVCC_1P2V domain of the
imx6sl SoC, so we need to keep it always powered.
According to imx6sl datasheet the GPIO block has three supplies:
NVCC33_IO, NVCC18_IO and NVCC_1P2V and it states that:
"All digital I/O supplies (NVCC_xxxx) must be powered under normal conditions
whether the associated I/O pins are in use or not"
This problem has been observed by the fact that a GPIO connected to an LED could
not work when the PMIC driver was enabled.
Keeping VGEN1 regulator always enabled fixes the problem.