Documentation: Fix x86_64 UEFI outdated references to elilo

Problem: The x86_64 UEFI doc references Elilo which is an
unmaintained/orphaned bootloader project. Also, on x86_64 a bootloader
is technically not actually required since there is support for the
Linux EFI stub.

Solution: Remove the references to Elilo from the doc and refer to the
EFI stub doc page, update steps accordingly, and add more details about
creation of the EFI partition to improve clarity.

Signed-off-by: Nir Lichtman <nir@lichtman.org>
Link: https://lore.kernel.org/r/20250108113522.GA897677@lichtman.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/arch/x86/x86_64/uefi.rst

@@ -12,14 +12,20 @@ with EFI firmware and specifications are listed below.
 
 1. UEFI specification:  http://www.uefi.org
 
-2. Booting Linux kernel on UEFI x86_64 platform requires bootloader
-   support. Elilo with x86_64 support can be used.
+2. Booting Linux kernel on UEFI x86_64 platform can either be
+   done using the <Documentation/admin-guide/efi-stub.rst> or using a
+   separate bootloader.
 
 3. x86_64 platform with EFI/UEFI firmware.
 
 Mechanics
 ---------
 
+Refer to <Documentation/admin-guide/efi-stub.rst> to learn how to use the EFI stub.
+
+Below are general EFI setup guidelines on the x86_64 platform,
+regardless of whether you use the EFI stub or a separate bootloader.
+
 - Build the kernel with the following configuration::
 
 	CONFIG_FB_EFI=y
@@ -31,16 +37,27 @@ Mechanics
 	CONFIG_EFI=y
 	CONFIG_EFIVAR_FS=y or m		# optional
 
-- Create a VFAT partition on the disk
-- Copy the following to the VFAT partition:
+- Create a VFAT partition on the disk with the EFI System flag
+    You can do this with fdisk with the following commands:
+
+        1. g - initialize a GPT partition table
+        2. n - create a new partition
+        3. t - change the partition type to "EFI System" (number 1)
+        4. w - write and save the changes
+
+    Afterwards, initialize the VFAT filesystem by running mkfs::
+
+        mkfs.fat /dev/<your-partition>
+
+- Copy the boot files to the VFAT partition:
+    If you use the EFI stub method, the kernel acts also as an EFI executable.
+
+    You can just copy the bzImage to the EFI/boot/bootx64.efi path on the partition
+    so that it will automatically get booted, see the <Documentation/admin-guide/efi-stub.rst> page
+    for additional instructions regarding passage of kernel parameters and initramfs.
 
-	elilo bootloader with x86_64 support, elilo configuration file,
-	kernel image built in first step and corresponding
-	initrd. Instructions on building elilo and its dependencies
-	can be found in the elilo sourceforge project.
+    If you use a custom bootloader, refer to the relevant documentation for help on this part.
 
-- Boot to EFI shell and invoke elilo choosing the kernel image built
-  in first step.
 - If some or all EFI runtime services don't work, you can try following
   kernel command line parameters to turn off some or all EFI runtime
   services.