arm64: remove __dma_*_area() aliases

The __dma_inv_area() and __dma_clean_area() aliases make cache.S harder
to navigate, but don't gain us anything in practice.

For clarity, let's remove them along with their redundant comments. The
only users are __dma_map_area() and __dma_unmap_area(), which need to be
position independent, and can call __pi_dcache_inval_poc() and
__pi_dcache_clean_poc() directly.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20211206124715.4101571-4-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>