spi: atmel-quadspi: Create `atmel_qspi_ops` to support newer SoC families

Refactor the code to introduce an ops struct, to prepare for merging
support for later SoCs, such as SAMA7G5. This code was based on the
vendor's kernel (linux4microchip). Cc'ing original contributors.

Signed-off-by: Csókás, Bence <csokas.bence@prolan.hu>
Link: https://patch.msgid.link/20241128174316.3209354-2-csokas.bence@prolan.hu


Signed-off-by: Mark Brown <broonie@kernel.org>