Documentation: serial: dedup kernel-doc for uart functions

Some of the serial (uart_*) functions are documented twice. Once as
kernel-doc along their sources and once in Documentation. So deduplicate
these texts, merge them into kernel-doc in the sources, and link them
using kernel-doc: from the Documentation.

To be properly linked and rendered, tabulators had to be removed from
the comments.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220728061056.20799-2-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>