docs: efi: add CPER functions to driver-api

There are two kernel-doc like descriptions at cper, which is used
by other parts of cper and on ghes driver. They both have kernel-doc
like descriptions.

Change the tags for them to be actual kernel-doc tags and add them
to the driver-api documentaion at the UEFI section.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Acked-by: Borislav Petkov (AMD) <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>

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

···
 .. SPDX-License-Identifier: GPL-2.0
 
-============
-UEFI Support
-============
+====================================================
+Unified Extensible Firmware Interface (UEFI) Support
+====================================================
 
 UEFI stub library functions
 ===========================
 
 .. kernel-doc:: drivers/firmware/efi/libstub/mem.c
    :internal:
+
+UEFI Common Platform Error Record (CPER) functions
+==================================================
+
+.. kernel-doc:: drivers/firmware/efi/cper.c

drivers/firmware/efi/cper.c

···
 }
 EXPORT_SYMBOL_GPL(cper_severity_str);
 
-/*
+/**
  * cper_print_bits - print strings for set bits
  * @pfx: prefix for each line, including log level and prefix string
  * @bits: bit mask