mxser: decrypt FCR values

Currently, some of the values written to FCR are magic constants. But
they are composed of well-defined bits. Use these named macros in place
of the constants.

No changes in objdump -d.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210618061516.662-62-jslaby@suse.cz


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