The code, which waits for fifo slot, has been extracted from
imx_pwm_config_v2 function and moved to new one - imx_pwm_wait_fifo_slot().

This change reduces the overall size of imx_pwm_config_v2() and prepares
it for atomic PWM operation.
Suggested-by: NStefan Agner <stefan@agner.ch>
Suggested-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: NLukasz Majewski <l.majewski@majess.pl>
Reviewed-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: NThierry Reding <thierry.reding@gmail.com>