iio: adc: rockchip_saradc: Allow compile-testing with !ARM

There seems no reason to allow for compile-testing on ARM only, so
remove this restriction.

Build-tested with allyesconfig on x86.

Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20200904170416.16061-1-alex.dewar90@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>