mach-integrator: fix VGA base regression

The changes introduced in commit
cc22b4c18540e5e8bf55c7d124044f9317527d3c
"ARM: set vga memory base at run-time"

Makes the Integrator/AP freeze completely. I appears that
this is due to the VGA base address being assigned at PCI
init time, while this base is needed earlier than that.
Moving the initialization of the base address to the
.map_io function solves this problem.

Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>