phy: marvell: ARMADA375_USBCLUSTER_PHY should not default to y, unconditionally

Merely enabling CONFIG_COMPILE_TEST should not enable additional code.
To fix this, restrict the automatic enabling of ARMADA375_USBCLUSTER_PHY
to MACH_ARMADA_375, and ask the user in case of compile-testing.

Fixes: eee47538 ("phy: add support for USB cluster on the Armada 375 SoC")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210208150252.424706-1-geert+renesas@glider.be


Signed-off-by: Vinod Koul <vkoul@kernel.org>