dtoc: Add a way to read a phandle with params

Add a function to read a phandle and associated name and offset. This is
useful for binman.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/test_dtoc.py b/tools/dtoc/test_dtoc.py
index 879ca2a..c62fcba 100755
--- a/tools/dtoc/test_dtoc.py
+++ b/tools/dtoc/test_dtoc.py
@@ -929,6 +929,7 @@
         self._check_strings(HEADER + '''
 struct dtd_source {
 \tstruct phandle_2_arg clocks[4];
+\tunsigned char	phandle_name_offset[13];
 };
 struct dtd_target {
 \tfdt32_t\t\tintval;
@@ -981,6 +982,8 @@
 \t\t\t{0, {11}},
 \t\t\t{1, {12, 13}},
 \t\t\t{4, {}},},
+\t.phandle_name_offset	= {0x0, 0x0, 0x0, 0x3, 0x66, 0x72, 0x65, 0x64,
+\t\t0x0, 0x0, 0x0, 0x0, 0x7b},
 };
 U_BOOT_DRVINFO(phandle_source) = {
 \t.name\t\t= "source",