Make indirect vectors addresses global, so they can be replaced by
various code that needs to do so. For example the MX6 PCI express
driver needs to temporarily replace data abort handler when reading
the config space.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Eric Nelson <eric.nelson@boundarydevices.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>