Support textlines in the configuration editor.

Signed-off-by: Simon Glass <sjg@chromium.org>

At present cedit only supports menu keys. For textline objects we need
to insert normal ASCII characters.

We also need to handle backspace, which is ASCII 9.

In fact, expo does not make use of all the menu keys, so partition
them accordingly and update the logic to support normal ASCII
characters, too.

Signed-off-by: Simon Glass <sjg@chromium.org>

When the devicetree is too small for the property being written, we need
to expand the devicetree and retry the write.

Put this logic into a function so it can be reused.

Signed-off-by: Simon Glass <sjg@chromium.org>

In a lot of cases menus are the only objects which are have their own
behaviour in the cedit, e.g. to move between menus. With expo expanding
to support text, this is no-longer true.

Use a switch() statement so that we can simply insert a new 'case' for
the new object types.

Signed-off-by: Simon Glass <sjg@chromium.org>

This internal function could use a comment. Add one.

Also tidy up a few other comments.

Signed-off-by: Simon Glass <sjg@chromium.org>

fixup: comments

Add a command to read edit settings from CMOS RAM, using the cedit
definition to indicate which registers and bits are used.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a command to write cedit settings to CMOS RAM so that it can be
preserved across a reboot. This uses a simple bit-encoding, where each
field has a 'bit position' and a 'bit length' in the schema.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a command to read cedit settings from environment variables so that
they can be restored as part of the environment.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a command to write cedit settings to environment variables so that
they can be stored with 'saveenv'.

Signed-off-by: Simon Glass <sjg@chromium.org>

Add a command to read cedit settings from a devicetree file.

Signed-off-by: Simon Glass <sjg@chromium.org>