Add missing TAILQ initializer (omitted in r250634).

Submitted by:	Zbigniew Bodek <zbb@semihalf.com>
Reviewed by:	alc
Sponsored by:	The FreeBSD Foundation, Semihalf
Provide settings for superpage reservation system on ARM.

This allows for enabling and configuring superpages reservation mechanism in
order to allocate and populate 256 4KB base pages (for the purpose of
promotion to a 1MB superpage).

Submitted by:	Zbigniew Bodek <zbb@semihalf.com>
Reviewed by:	alc
Sponsored by:	The FreeBSD Foundation, Semihalf