powerpc/52xx: Mark gpt driver as not removable

Returning an error code (here -EBUSY) from a remove callback doesn't
prevent the driver from being unloaded. The only effect is that an error
message is emitted and the driver is removed anyhow.

So instead drop the remove function (which is equivalent to returning zero)
and set the suppress_bind_attrs property to make it impossible to unload
the driver via sysfs.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220612213400.159257-1-u.kleine-koenig@pengutronix.de