spi: rspi: Relax DMA dependency and increase build coverage

As of commit ab116a4d ("dmaengine:
shdma: fix a build failure on platforms with no DMA support"), the DMA
filter function shdma_chan_filter() is sufficiently abstracted to allow
building without DMA support. Hence drop the SH_DMAE_BASE dependency on
SUPERH.
Also increase build coverage by allowing the driver to be enabled if
COMPILE_TEST=y.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@linaro.org>