kconfig: Avoid potential issue parsing generated_dts_board.conf

Splitting a string like 'foo="bar=baz"' on '=' will give ['foo', '"bar',
'baz"'] instead of the intended ['foo', '"bar=baz"']. split() with
maxsplit=1 to avoid potential issues.

Not seen in practice. Just some future safety.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/kconfig/kconfigfunctions.py

@@ -20,7 +20,7 @@
         with open(GENERATED_DTS_BOARD_CONF, 'r', encoding='utf-8') as fd:
             for line in fd:
                 if '=' in line:
-                    define, val = line.split('=')
+                    define, val = line.split('=', 1)
                     dt_defines[define] = val.strip()
 
 def _dt_units_to_scale(unit):