FROMLIST: tools/bootconfig: Support mixed value and subkey test cases

Update test case to support mixed value and subkey on a key.

Picking this up FROMLIST to get the fix ASAP. It is likely to be
accepted upstream.

Signed-off-by: Devin Moore <devinmoore@google.com>
Link: https://lore.kernel.org/lkml/162262192121.264090.6540508908529705156.stgit@devnote2/
Bug: 183237066
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Change-Id: I42bb63afb9d7c3e3cd3e3c3a87d41db59bf27043

tools/bootconfig/samples/bad-override.bconf

@@ -1,3 +0,0 @@
-key.subkey = value
-# We can not override pre-defined subkeys with value
-key := value

tools/bootconfig/samples/bad-override2.bconf

@@ -1,3 +0,0 @@
-key = value
-# We can not override pre-defined value with subkey
-key.subkey := value

tools/bootconfig/samples/good-mixed-append.bconf

@@ -0,0 +1,4 @@
+key = foo
+keyx.subkey = value
+key += bar
+

tools/bootconfig/samples/good-mixed-kv3.bconf

@@ -0,0 +1,6 @@
+# mixed key and subkeys with braces
+key = value
+key {
+	subkey1
+	subkey2 = foo
+}

tools/bootconfig/samples/good-mixed-override.bconf

@@ -0,0 +1,4 @@
+key.foo = bar
+key = value
+# mixed key value can be overridden
+key := value2