counter: Introduce the COUNTER_COMP_FREQUENCY() macro

Now that there are two users for the "frequency" extension, introduce a
new COUNTER_COMP_FREQUENCY() macro.
This extension is intended to be a read-only signal attribute.

Suggested-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20240306153631.4051115-1-fabrice.gasnier@foss.st.com


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