efi/libstub: Add libstub/mem.c to the documentation tree

Let the description of the efi/libstub/mem.c functions appear in the kernel
API documentation in the following chapters:

The Linux driver implementer’s API guide
Linux Firmware API
UEFI Support
UEFI stub library functions

Acked-by: Jonathan Corbet <[e-mail]>
Signed-off-by: Heinrich Schuchardt <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/r/[e-mail]

Documentation/driver-api/firmware/efi/index.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+UEFI Support
+============
+
+UEFI stub library functions
+===========================
+
+.. kernel-doc:: drivers/firmware/efi/libstub/mem.c
+   :internal:

Documentation/driver-api/firmware/index.rst

···
 
    introduction
    core
+   efi/index
    request_firmware
    other_interfaces