video: Move HP PARISC STI core code to shared location

STI core files have been located in console and fbdev code. Move
the source code and header to the directories for video helpers.
Also update the config and build rules such that the code depends
on the config symbol CONFIG_STI_CORE, which STI console and STI
framebuffer select automatically.

Cleans up the console makefile and prepares PARISC to implement
fb_is_primary_device() within the arch/ directory. No functional
changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230417125651.25126-12-tzimmermann@suse.de