doc: riscv: rv32m1_vega: add BLE software link layer info
doc: riscv: rv32m1_vega: add BLE software link layer info

Since the experimental BLE software link layer is enabled on
the VEGABoard, add some information about it, as well as the
limitations.

Signed-off-by: Alex Porosanu <9cd4fe7678e1630676677a8799e6ca36cabb4300@nxp.com>

zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr