ARM: MX3: make CPU revision number detection work on all boards

Commit 52939c03

 (ARM: MX3: fix CPU revision number detection) started
using the CPU's SREV register for revision number detection. This
makes it mandatory to have a valid SPBA0 mapping. Add this to the
global map_io code instead of adding multiple copies for each board.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Daniel Mack <daniel@caiaq.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>

Tested on Qong (EVB-Lite)
Tested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>