vme: Convert VME core to register as a subsystem

Previously, VME bridge support was treated as any other driver (using
module_init() macro), but if VME bridge and vme_user (staging) drivers
were compiled into the kernel, then vme_user would attempt to register
itself before the VME core support had been loaded. This would result
in a kernel panic.

The load order of these built-in drivers is based on the order in which
drivers/staging/vme and driver/vme are compiled.

This patch changes the VME core driver to use the subsys_initcall()
macro which ensures that it is loaded before all other VME drivers
regardless of the order in which they are compiled.

Tested-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Martyn Welch <martyn.welch@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>