Documentation: MXS: general update and improvements ...

Go more into detail about the relationship of the prepare stage and the
bootloader image, and about the generated images. Also don't use
mxs-usb-loader anymore since it has been removed.

Fixes: 3ca576cc4a4236a2556ab17 "scripts: imx/mxs remove mxs-usb-loader"
Signed-off-by: Roland Hieber <r.hieber@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: remove :numbered: from lower level toctrees ...

Only the highest level toctree may have :numbered:, otherwise
sphinxs complains loudly that the subtree is already numbered.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

docs: fix hiding of chapter from imx.rst ...

The files 'mxs.rst' and 'imx.rst' used the same chapter headline:

    Freescale i.MXs

This confuses sphinx. It does not support having the same headline at
the same level twice and hides the other chapter. Just rename the
chapter heading to avoid that.

And rename the subchapter headline to 'MXS boards' for clarity.

Signed-off-by: Stefan Lengfeld <contact@stefanchrist.eu>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

docs: fix typos ...

Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

docs: remove trailing whitespaces ...

Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Docs: move the individual MXS target documentation where they belong to ...

i.MX and MXS differs in their global documentation. Honor this.

Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Docs: extend the mentioned commands with a link to their documentation ...

Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Add documentation for booting Freescale MXS SoCs ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>