[DRIVER MODEL] Fix sgivwfb

Statically allocated devices in module data is a potential cause
of oopsen.  The device may be in use by a userspace process, which
will keep a reference to the device.  If the module is unloaded,
the module data will be freed.  Subsequent use of the platform
device will cause a kernel oops.

Use generic platform device allocation/release code in modules.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>