[build]: Fix marvell-armhf build hung issue (sonic-net#10156)

The marvel-armhf build is hung, it does not exist after waiting for a long time.
It is caused by the process /etc/entropy.py which is started by the postinst script in target/debs/buster/sonic-platform-nokia-7215_1.0_armhf.deb

$ cat postinst 
sh /usr/sbin/nokia-7215_plt_setup.sh
...

$ cat usr/sbin/nokia-7215_plt_setup.sh | tail

    python /etc/entropy.py &


$ cat etc/entropy.py 
if path.exists("/proc/sys/kernel/random/entropy_avail"):
    while 1:
        while avail() < 2048:
            with open('/dev/urandom', 'rb') as urnd, open("/dev/random", mode='wb') as rnd:
                d = urnd.read(512)
                t = struct.pack('ii', 4 * len(d), len(d)) + d
                fcntl.ioctl(rnd, RNDADDENTROPY, t)
        time.sleep(30)

It is a workaround to fix the build issue, need to fix debian package, and revert the change.

files/build_templates/sonic_debian_extension.j2

@@ -637,6 +637,11 @@ clean_proc() {
 }
 trap_push clean_proc
 sudo mount proc /proc -t proc
+if [[ $CONFIGURED_ARCH == armhf ]]; then
+    # A workaround to fix the armhf build hung issue, caused by sonic-platform-nokia-7215_1.0_armhf.deb post installation script 
+    ps -eo pid,cmd | grep python | grep "/etc/entropy.py" | awk '{print $1}' | xargs sudo kill -9 2>/dev/null || true
+fi
+
 sudo mkdir $FILESYSTEM_ROOT/target
 sudo mount --bind target $FILESYSTEM_ROOT/target
 sudo chroot $FILESYSTEM_ROOT docker $SONIC_NATIVE_DOCKERD_FOR_DOCKERFS info