libflashrom: Move documentation to header

The doxygen documentation was in the libflashrom.c file. Move the
documentation to the libflashrom.h file. This allows foreign function
interface binding generators (eg rust bindgen) that operate on the .h
file to generate documentation for the target language. Some doxygen
errors were also corrected, mostly undocumented or wrongly labeled
parameters.

To test, I have diffed and inspected the doxygen documentation before
and after the change. All functions are documented the same, and the
structs and enums are now also included in the docs.

Change-Id: I856b74d5bfea13722539be15496755a95e701eea
Signed-off-by: Evan Benn <evanbenn@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/63903
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>

Doxyfile

@@ -780,10 +780,7 @@ WARN_LOGFILE           =
 # spaces. See also FILE_PATTERNS and EXTENSION_MAPPING
 # Note: If this tag is empty the current directory is searched.
 
-INPUT                  = libflashrom.c \
-                         libflashrom.h \
-                         flashrom.c \
-                         layout.c \
+INPUT                  = include/libflashrom.h
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses