doc: Add a description for bootmeth_qfw

Add documentation for the qfw bootmeth.

Fix up the compatible string to drop the 'extlinux' part, which is not
relevant to this bootmeth.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
diff --git a/doc/develop/bootstd/overview.rst b/doc/develop/bootstd/overview.rst
index 6afa1c2..ef87896 100644
--- a/doc/develop/bootstd/overview.rst
+++ b/doc/develop/bootstd/overview.rst
@@ -423,6 +423,7 @@
    - VBE
    - EFI boot using boot manager
    - Android bootflow (boot image v4)
+   - :doc:`QFW <qfw>`: QEMU firmware interface
 
 Each driver is controlled by a Kconfig option. If no bootmeth driver is
 selected by a compatible string in the devicetree, all available bootmeth