misc: panel, convert struct to bitmap

There is an anonymous struct which is actually used as a bitmap. So
convert the struct to a bitmap and change code accordingly where
needed.

This also allows for a cleanup of set_data_bits and set_ctrl_bits as
they can use a common helper now. The helper can also be converted to
a for loop instead of doing bit OR. And given it is a for loop now,
bit masking (using BIT_MSK) is moved from the callers there too.

Signed-off-by: Daniel Chromik <daniel.chromik@seznam.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Ksenija Stanojevic <ksenija.stanojevic@gmail.com>
Acked-by: Willy Tarreau <willy@haproxy.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>