dmaengine: sh: Kconfig: Add ARCH_R9A07G054 dependency for RZ_DMAC config option

RZ/V2L DMA block is identical to one found on RZ/G2L SoC. This patch adds
ARCH_R9A07G054 dependency for RZ_DMAC config option so that the driver
can be enabled on RZ/V2L SoC. While at it, also update config help text.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220221224321.11939-1-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>