tests: drivers: comparator: gpio_loopback: extend to xg24 and xg29 boards

Add board overlays to execute the comparator gpio_loopback testsuite on
xg24_dk2601b and xg29_rb4412a. The testsuite was executed and was seen
to pass on both boards locally with twister.

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