binman: Add rST references for binman entry types

Add references in the documentation for each entry type, so we can refer
to them from other documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/entry.py b/tools/binman/entry.py
index a07a588..e3767ae 100644
--- a/tools/binman/entry.py
+++ b/tools/binman/entry.py
@@ -750,6 +750,11 @@
                 first_line = lines[0]
                 rest = [line[4:] for line in lines[1:]]
                 hdr = 'Entry: %s: %s' % (name.replace('_', '-'), first_line)
+
+                # Create a reference for use by rST docs
+                ref_name = f'etype_{module.__name__[6:]}'.lower()
+                print('.. _%s:' % ref_name)
+                print()
                 print(hdr)
                 print('-' * len(hdr))
                 print('\n'.join(rest))