counter: microchip-tcb-capture: Add support for RC Compare

In Capture mode, the RC register serves as a compare register for the
Timer Counter Channel. When a the Counter Value reaches the RC value, a
RC Compare event occurs (COUNTER_EVENT_THRESHOLD). This patch exposes
the RC register to userspace as the 'compare' Count extension, thus
allowing users to configure the threshold condition for these events.

Acked-by: Bence Csókás <csokas.bence@prolan.hu>
Link: https://lore.kernel.org/r/20250306-introduce-compare-component-v1-2-93993b3dca9c@kernel.org


Signed-off-by: William Breathitt Gray <wbg@kernel.org>