test/py: Add support for loading image via tftp to specified location

For example this setting:

env__net_tftp_readable_file = {
    "fn": "ep108/image.ub",
    "addr": 0x10000000,
    "size": 25846296,
    "crc32": "b726f9de",
}

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
diff --git a/test/py/tests/test_net.py b/test/py/tests/test_net.py
index 07393eb..4ab58b4 100644
--- a/test/py/tests/test_net.py
+++ b/test/py/tests/test_net.py
@@ -43,6 +43,7 @@
 # may be omitted or set to None if TFTP testing is not possible or desired.
 env__net_tftp_readable_file = {
     "fn": "ubtest-readable.bin",
+    "addr": 0x10000000,
     "size": 5058624,
     "crc32": "c2244b26",
 }
@@ -135,7 +136,10 @@
     if not f:
         pytest.skip('No TFTP readable file to read')
 
-    addr = u_boot_utils.find_ram_base(u_boot_console)
+    addr = f.get('addr', None)
+    if not addr:
+        addr = u_boot_utils.find_ram_base(u_boot_console)
+
     fn = f['fn']
     output = u_boot_console.run_command('tftpboot %x %s' % (addr, fn))
     expected_text = 'Bytes transferred = '