ArmPkg/ArmDmaLib: deal with NULL return value of UncachedAllocatePages ()
ArmPkg/ArmDmaLib: deal with NULL return value of UncachedAllocatePages ()

The allocation function UncachedAllocatePages () may return NULL, in
which case our implementation of DmaAllocateBuffer () should return
EFI_OUT_OF_RESOURCES rather than silently ignoring the NULL value and
returning EFI_SUCCESS.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <66d3c5fdaeea7ff1f996ad04f2c45e08ab38e2f5@linaro.org>
Reviewed-by: Leif Lindholm <a613079f0455438b29e28a9c5b9eb3779a81a33a@linaro.org>

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