arm: mvebu: Add missing "if SPL"

We can only select SPL_SKIP_LOWLEVEL_INIT if SPL is enabled, otherwise
we get a warning about unmet dependencies on platforms that don't use
SPL.

Fixes: cf47a8cf8f ("arm: mvebu: Select SPL_SKIP_LOWLEVEL_INIT on ARMADA_32BIT")
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stefan Roese <sr@denx.de>

arch/arm/mach-mvebu/Kconfig

@@ -11,7 +11,7 @@ config ARMADA_32BIT
 	select SPL_DM if SPL
 	select SPL_DM_SEQ_ALIAS if SPL
 	select SPL_OF_CONTROL if SPL
-	select SPL_SKIP_LOWLEVEL_INIT
+	select SPL_SKIP_LOWLEVEL_INIT if SPL
 	select SPL_SIMPLE_BUS if SPL
 	select SUPPORT_SPL
 	select TRANSLATION_OFFSET