dmaengine: mediatek: uart-apdma: Fix above 4G addressing TX/RX

dmaengine: mediatek: uart-apdma: Fix above 4G addressing TX/RX

The VFF_4G_SUPPORT register is named differently in datasheets,
and its name is "VFF_ADDR2"; was this named correctly from the
beginning it would've been clearer that there was a mistake in
the programming sequence.

This register is supposed to hold the high bits to support the
DMA addressing above 4G (so, more than 32 bits) and not a bit
to "enable" the support for VFF 4G.

Fix the name of this register, and also fix its usage by writing
the upper 32 bits of the dma_addr_t on it when the SoC supports
such feature.

Fixes: 9135408c3ace ("dmaengine: mediatek: Add MediaTek UART APDMA support")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patch.msgid.link/20251113122229.23998-6-angelogioacchino.delregno@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>