dmaengine: mv_xor: Allow selecting mv_xor for mvebu only compatible SoC

Armada 3700 SoC uses the mv_xor driver but don't select anymore the
PLAT_ORION symbol. This commit extends the dependency of the mv_xor
driver to the more modern SoCs only compatible with ARCH_MVEBU, which
allows using it with the Armada 3700 SoC.

In the same time it also add the COMPILE_TEST dependency allowing a wider
test coverage.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>