ovmerge: Support literal assignments of path strings

The dtc compiler expands &node1 (as opposed to <&node1>) to the full
path to the node with the label "node1". Note that if this label is on
a node in an overlay that the path will reflect that, even if the
node with the label eventually ends up in the base dtb.

If a parameter of a base dts is used to make an alias point to another
node in the base dts, it is nice to be able to specify that replacement
path using a label on that node, rather than have to write it out
longhand. Doing so requires one simple change - treating literal
assignments of empty strings as a special case:

    console_uart0 = <&aliases>, "console=", &uart0;

Prior to this commit, this would have resulted in an error when the
dts file was parsed because the &uart0 path string would have been
interpreted as a malformed refence to the next override target.
With this commit, the parser sees the empty string assigment and
treats the next thing as a string to assign (rather like assigning
a phandle value to an integer property).

A consequence of this change is that intentionally assigning an empty
string (probably a very rare occurence) requires an explicit empty
string to be added, i.e. "...=","" or that the empty assignment falls
at the end of the list of overrides for that parameter.

Author: pelwell

ovmerge/ovmerge

@@ -721,7 +721,19 @@ sub dtparam
 				my $val = $value;
 				if ($op eq '=')
 				{
-					$val = $opdata;
+					if ($opdata ne '')
+					{
+						$val = $opdata;
+					}
+					elsif ($pos == @$ovr)
+					{
+						$val = "";
+					}
+					else
+					{
+						$val = $ovr->[$pos++];
+						die "* Expected a string or label reference in parameter '$param'\n" if (($val->[0] ne '"') && ($val->[0] ne '&'));
+					}
 				}
 				elsif ($op eq '{')
 				{
@@ -735,7 +747,7 @@ sub dtparam
 					}
 					else
 					{
-						apply_prop($node, $prop, ['"', $val]);
+						apply_prop($node, $prop, ref($val) ? $val : [ '"', $val ]);
 					}
 				}
 			}