sw: update firmware build script

• update build script with config to turn on PA
• update mikrobus-greybus submodule with beagleconnect freedom config

sensortest :

vaishnav@spectre:~/freedom/beagleconnect/sw$ ./test-net.sh
ping6 -I lowpan0 ff02::1 -c 5
+ ping6 -I lowpan0 ff02::1 -c 5
ping6: Warning: source address might be selected on device other than: lowpan0
PING ff02::1(ff02::1) from :: lowpan0: 56 data bytes
64 bytes from fe80::1eee:b121:4b:1200%lowpan0: icmp_seq=1 ttl=64 time=53.8 ms
64 bytes from fe80::1eee:b121:4b:1200%lowpan0: icmp_seq=2 ttl=64 time=30.0 ms
64 bytes from fe80::1eee:b121:4b:1200%lowpan0: icmp_seq=3 ttl=64 time=30.1 ms
64 bytes from fe80::1eee:b121:4b:1200%lowpan0: icmp_seq=4 ttl=64 time=29.9 ms
64 bytes from fe80::1eee:b121:4b:1200%lowpan0: icmp_seq=5 ttl=64 time=30.0 ms

--- ff02::1 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4004ms
rtt min/avg/max/mdev = 29.920/34.745/53.792/9.523 ms
vaishnav@spectre:~/freedom/beagleconnect/sw$ python3 ./sensortest-rx.py
('fe80::1eee:b121:4b:1200', 49475, 0, 8)  b'3l: 29.780000;4x:-7.660800;4y:-1.225728;4z:-5.362560;5h: 54.255676;5t: 26.107254'
('fe80::1eee:b121:4b:1200', 49475, 0, 8)  b'3l: 29.570000;4x:-7.507584;4y:-1.378944;4z:-5.209344;5h: 54.199218;5t: 26.180267'
^CTraceback (most recent call last):
  File "./sensortest-rx.py", line 15, in <module>
    data, sender = sock.recvfrom(1024)
KeyboardInterrupt