counter: 104-quad-8: Utilize helper functions to handle PR, FLAG and PSC

The Preset Register (PR), Flag Register (FLAG), and Filter Clock
Prescaler (PSC) have common usage patterns. Wrap up such usage into
dedicated functions to improve code clarity.

Link: https://lore.kernel.org/r/a2d663337bf2907e0283023c06b1ddcbb32f7f6d.1681753140.git.william.gray@linaro.org/


Signed-off-by: William Breathitt Gray <william.gray@linaro.org>