MFC r309823:

[evdev] Adds evdev support to sysmouse(4) driver

For horizontal (T-axis) wheel reporting which is not supported by
sysmouse protocol kern.evdev.sysmouse_t_axis sysctl is introduced.
It can take following values:

0 - no T-axis events (default)
1 - T-axis events are originated in ums(4) driver.
2 - T-axis events are originated in psm(4) driver.

Submitted by: Vladimir Kondratiev <wulf@cicgroup.ru>
Differential Revision: https://reviews.freebsd.org/D8597