spi: stm32-qspi: Add dirmap support

Add stm32_qspi_dirmap_read() and stm32_qspi_dirmap_create()
to get dirmap support.

Update the exec_op callback which doens't allow anymore memory map
access. Memory map access are only available through the dirmap_read
callback.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20210419121541.11617-4-patrice.chotard@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>