clk/qcom: apq8016: allow apq8016_clk_init_uart() to be called externally

clk/qcom: apq8016: allow apq8016_clk_init_uart() to be called externally

When U-Boot as running as the first stage bootloader on MSM8916 devices,
early debug UART requires turning on the clocks (for some reason the
pre-loader turns them off?!).

To simplify developing for this platform, allow the
apq8016_clk_init_uart() function to be called externally. Developers can
call this from the serial_msm debug uart driver to configure the clocks
before the driver model is available.

As it is only possible to enable early debug UART in custom builds of
U-Boot, this solution at least gives developers the option.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>