drm/armada: move armada_drm_mode_config_funcs to armada_drv.c

Move the armada_drm_mode_config_funcs to armada_drv.c, since this now
has less to do with FBs than it does with general mode configuration.
In doing so, we need to make armada_fb_create() visible to armada_drv.c,
which reveals a function name clash with armada_fbdev.c.  Rename the
version in armada_fbdev.c.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>