ArmPkg: remove UncachedMemoryAllocationLib

ArmPkg: remove UncachedMemoryAllocationLib

Now that ArmDmaLib can take care of its own memory allocation needs,
let's get rid of UncachedMemoryAllocationLib entirely. This forces
platforms to declare the required semantics (non-cache coherent DMA,
whichever way it is implemented), rather than using uncached memory
allocations directly, which may not always be the right choice, and
prevents sharing of drivers between platforms if one is cache coherent
and the other is not.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>