evdev: Hide "kern.evdev.rcpt_mask" sysctl if kernel is compiled
w/o EVDEV_SUPPORT as it's value has no meaning in this case.

Now presence of this sysctl can be used for discovery if evdev support
for hybrid devices is compiled into kernel or not.
Hide "kern.evdev.sysmouse_t_axis" sysctl for the same reason.

Reviewed by: gonzo
Approved by: gonzo (mentor)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D12676