vt: Draw logos per CPU core

This feature is inspired by another Unix-alike OS commonly found on
airplane headrests.

A number of beasties[0] are drawn at top of framebuffer during boot,
based on the number of active SMP CPUs[1]. Console buffer output
continues to scroll in the screen area below beastie(s)[2].

After some time[3] has passed, the beasties are erased leaving the
entire terminal for use.

Includes two 80x80 vga16 beastie graphics and an 80x80 vga16 orb
graphic. (The graphics are RLE compressed to save some space -- 3x 3200
bytes uncompressed, or 4208 compressed.)

[0]: The user may select the style of beastie with

kern.vt.splash_cpu_style=(0|1|2)

[1]: Or the number may be overridden with tunable kern.vt.splash_ncpu.
[2]: https://www.youtube.com/watch?v=UP2jizfr3_o
[3]: Configurable with kern.vt.splash_cpu_duration (seconds, def. 10).

Differential Revision: https://reviews.freebsd.org/D2181
Reviewed by: dumbbell, emaste
Approved by: markj (mentor)
MFC after: 2 weeks