Orion: revamp cpu mbus window handling

Instead of forcing all device bus window setup through one function
with some enum as the first argument, create separate window setup
functions for each of the four possible targets, and do the demux
internally.  This allows getting rid of the window identifier enum
and the big switch statement in orion_setup_cpu_win().

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Reviewed-by: Tzachi Perelstein <tzachi@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Nicolas Pitre <nico@marvell.com>