doc: Bluetooth dev: Fix mention of nrf52 not supporting split builds

Since #67318 we support split builds in the simulated nRF52
over the UART, and we actually have this configuration
tested in CI.
This documentation paragraph was still mentioning this is not
supported. So let's fix it.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>