dt-bindings: arm: l2x0: Tauros 3 is PL310 compatible

The validation is unhappy about mmp3-dell-ariel declaring its
marvell,tauros3-cache node to be compatible with arm,pl310-cache:

  mmp3-dell-ariel.dt.yaml: cache-controller@d0020000: compatible:
       Additional items are not allowed ('arm,pl310-cache' was unexpected)
  mmp3-dell-ariel.dt.yaml: cache-controller@d0020000: compatible:
       ['marvell,tauros3-cache', 'arm,pl310-cache'] is too long

Let's allow this -- Tauros 3 is designed to be compatible with PL310.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
[robh: fixup indentation]
Signed-off-by: Rob Herring <robh@kernel.org>