hwrng: meson - 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/char/hw_random/meson-rng.ko | grep alias
alias:          platform:meson-rng

After this patch:

$ modinfo drivers/char/hw_random/meson-rng.ko | grep alias
alias:          platform:meson-rng
alias:          of:N*T*Camlogic,meson-rngC*
alias:          of:N*T*Camlogic,meson-rng

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>