imx: ventana: split out common functions between SPL and uboot
Move shared functions used by both SPL and U-Boot to common.c:
- setup_iomux_uart() and uart pad config
- gpio pad config
In the process also moved the following to common.c in preparation for
calling it from the SPL:
- split i2c setup into a shared function
- move pmic init to setup_pmic() function to call directly from
power_init_board()
- split gpio setup into early (iomux and default pin config)
and late (output configuration based on env)
