char: xillybus: remove direct dependency on DT functions

Drivers generally should not need to depend directly on OF_ADDRESS or
OF_IRQ. Convert xillybus to use the preferred platform_get_resource() and
platform_get_irq() functions to remove this dependency.

Cc: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>