serial: pic32: move header content to .c

There is no point keeping the header content separated. So move the
content to the appropriate source file.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220503063122.20957-3-jslaby@suse.cz


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