ARM926: remove exports and forward decls

Unneeded exports cause confusion about the module interfaces.
Only the Feroceon code builds on this, so only routines it
reuses should be public..  Make most remaining functions
static, and fix some of the line-too-long issues.

The forward decls are just code clutter; move their references
later, after the normal declarations.  Turns out we don't need
even one forward declaration in this file.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>