ref-manual: Describe grub-efi-cfg overrides and GRUB_TITLE

This patch describes how to use overrides for grub-efi-cfg because that
is otherwise only clear after reading the .bbclass file. It also adds
a description for GRUB_TITLE.

(From yocto-docs rev: b9ec7d124c9cbaf6c05415277fa028a39ce9e02f)

Signed-off-by: "Simon A. Eugster" <simon.eu@gmail.com>
Reviewed-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/classes.rst

@@ -1048,6 +1048,7 @@ This class supports several variables:
 
 -  :term:`INITRD`: Indicates list of filesystem images to
    concatenate and use as an initial RAM disk (initrd) (optional).
+   Can be specified for each ``LABEL``.
 
 -  :term:`ROOTFS`: Indicates a filesystem image to include
    as the root filesystem (optional).
@@ -1061,6 +1062,9 @@ This class supports several variables:
 -  :term:`APPEND`: An override list of append strings for
    each ``LABEL``.
 
+-  :term:`GRUB_TITLE`: A custom title for each ``LABEL``. If a label does not
+   have a custom title, the label is used as title for the GRUB menu entry.
+
 -  :term:`GRUB_OPTS`: Additional options to add to the
    configuration (optional). Options are delimited using semi-colon
    characters (``;``).
@@ -1068,6 +1072,18 @@ This class supports several variables:
 -  :term:`GRUB_TIMEOUT`: Timeout before executing
    the default ``LABEL`` (optional).
 
+Each ``LABEL`` defined in the :term:`LABELS` variable creates a GRUB boot
+entry, and some variables can be defined individually per ``LABEL``. The label
+specific override names are defined as ``grub_LABEL``.
+
+For example, for a label ``factory``, the override name would be
+``grub_factory``. A custom GRUB menu entry titled "Factory Install" with the
+additional parameter ``factory=yes`` can be achieved as follows::
+
+   LABELS:append = " factory"
+   APPEND:grub_factory = "factory=yes"
+   GRUB_TITLE:grub_factory = "Factory Install"
+
 .. _ref-classes-gsettings:
 
 ``gsettings``

documentation/ref-manual/variables.rst

@@ -3382,6 +3382,11 @@ system and gives an overview of their function and contents.
       :ref:`ref-classes-grub-efi` class for more information
       on how this variable is used.
 
+   :term:`GRUB_TITLE`
+      Specifies custom titles for GRUB labels defined in  :term:`LABELS`. See
+      the :ref:`ref-classes-grub-efi` class for more information on how this
+      variable is used.
+
    :term:`GTKIMMODULES_PACKAGES`
       When inheriting the :ref:`ref-classes-gtk-immodules-cache` class,
       this variable specifies the packages that contain the GTK+ input