spi: xlp: Fix module autoload for OF registration

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/spi/spi-xlp.ko | grep alias
alias:          acpi*:BRCM900D:*

After this patch:

$ modinfo drivers/spi/spi-xlp.ko | grep alias
alias:          acpi*:BRCM900D:*
alias:          of:N*T*Cnetlogic,xlp832-spiC*
alias:          of:N*T*Cnetlogic,xlp832-spi

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>