xtensa: xtfpga: fix definitions of platform devices

commit a558d99263936b8a67d4eff8918745a77bfd8c31 upstream.

Remove __initdata attribute, as the devices may be used after init
sections are freed.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>