Input: avoid BIT() macro usage in the serio.h UAPI header

The commit 19ba1eb1 ("Input: psmouse - add a custom serio protocol
to send extra information") introduced usage of the BIT() macro
for SERIO_* flags; this macro is not provided in UAPI headers.
Replace if with similarly defined _BITUL() macro defined
in <linux/const.h>.

Fixes: 19ba1eb1

 ("Input: psmouse - add a custom serio protocol to send extra information")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Cc: <stable@vger.kernel.org> # v5.0+
Link: https://lore.kernel.org/r/20200324041341.GA32335@asgard.redhat.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>