spi: spi-imx: add support for SPI_RX_CPHA_FLIP

When SPI_RX_CPHA_FLIP is set, flip CPHA on Rx only transfers. This is
useful to access devices that use inverted CPHA for MISO vs MOSI
signals.

Only support the mx51/mx53 variants for now.

Tested on i.MX6ULL based system.

Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
Link: https://lore.kernel.org/r/e11b4446afe9a46a282dd923d22c27d03fae15f8.1649702729.git.baruch@tkos.co.il
Signed-off-by: Mark Brown <broonie@kernel.org>