staging: fbtft: Fix module autoload

If the driver is built as a module, autoload won't work because the module
alias information is not filled. So user-space can't match the registered
device with the corresponding module.

Export the module alias information using the MODULE_DEVICE_TABLE() macro.

Before this patch:

$ modinfo drivers/staging/fbtft/flexfb.ko | grep alias
$

After this patch:

$ modinfo drivers/staging/fbtft/flexfb.ko | grep alias
alias:          platform:flexpfb

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>