Vc-mem debug tidyup

This is a small tidyup of the vc-mem driver.

- removes broken procfs code (which was generating a warning, was no longer being compiled and should not be used) replacing it with debugfs equivalents. The facility for retriggering scanning of the VC image is removed as it doesn't seem especially useful (and had been #ifdef'd out without anyone complaining).

- replace printk() with pr_XXX(). We're not supposed to use printk() directly anymore, plus pr_XXX() can be enabled at compile-time per-module, or using dynamic debug at run-time (if enabled in the build).