arm: mvebu: Fix Kconfig dependency warnings

arm: mvebu: Fix Kconfig dependency warnings

We now have MEVBU boards without SPL support (e.g. db-xc3-24g4xg).
Because of this, a new compile time warning from Kconfig is show:

WARNING: unmet direct dependencies detected for SPL_OF_CONTROL
  Depends on [n]: SUPPORT_OF_CONTROL [=y] && SPL [=n] && OF_CONTROL [=y]
  Selected by [y]:
  - ARMADA_32BIT [=y] && ARM [=y] && ARCH_MVEBU [=y]

WARNING: unmet direct dependencies detected for SPL_DM
  Depends on [n]: DM [=y] && SPL [=n]
  Selected by [y]:
  - ARMADA_32BIT [=y] && ARM [=y] && ARCH_MVEBU [=y]
...

This patch fixes this issue and removes these warnings.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Chris Packham <judge.packham@gmail.com>