spi: stm32-qspi: add dma support

This patch adds the dma support for the stm32-qspi hardware.
The memory buffer constraints (lowmem, vmalloc, kmap) are taken into
account by framework. In read mode, the memory map is preferred vs
dma (due to better throughput). If the dma transfer fails the buffer
is sent by polling.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>