binman: Support adding sections to FMAPs

When used with hierarchical images, use the Chromium OS convention of
adding a section before all the subentries it contains.

BUG=b:184146709
TEST=binman test

Signed-off-by: Simon Glass <sjg@chromium.org>
Change-Id: I2ff03fd22106f4301e526765f932354b9eaa5e24
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/u-boot/+/2803414
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
4 files changed