it8xxx2: fix build with CONFIG_SOC_IT8XXX2_PLL_FLASH_48M=n
it8xxx2: fix build with CONFIG_SOC_IT8XXX2_PLL_FLASH_48M=n

The chip I2C driver uses chip_get_pll_freq(), so that function needs to
be built even when the PLL configuration is not changed at boot.

Signed-off-by: Peter Marheine <ef0b2c492edde94778d7465bfbaeed52c5be6858@chromium.org>

galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr