boards: silabs: update board support for comparator driver

The xg24_dk2601b, xg24_ek2703a, xg27_dk2602a, xg23_rb4210a,
xg24_rb4187c and xg29_rb4412a board yaml files were updated
to support the comparator driver. Documentation hardware
support was updated for each of these boards as well to
mention support for the ACMP hardware block and comparator
driver.

Signed-off-by: Christian Galante <christian.galante@silabs.com>