gpio: aggregator: unify function naming

gpio: aggregator: unify function naming

Unify function names to use gpio_aggregator_ prefix (except GPIO
forwarder implementations, which remain unchanged in subsequent
commits). While at it, rename the pre-existing gpio_aggregator_free() to
gpio_aggregator_destory(), since that name will be used by new
alloc/free functions introduced in the next commit, for which the name
is more appropriate.

No functional change.

Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Link: https://lore.kernel.org/r/20250407043019.4105613-3-koichiro.den@canonical.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>