Revert "spi: i.MX: optimize transfers for ECSPI v2.3" ...

This does not work on the Efika MX Smartbook which uses SPI
to connect the MC13892. Needs some rework.

This reverts commit 746a553.

spi: i.MX: optimize transfers for ECSPI v2.3 ...

Instead of writing one word to the txfifo and then wait until
one is received in the rxfifo we can write until the txfifos
are not full and read as long the rxfifos contain data. This
makes transfers for the m25p80 driver around 7 times faster
here.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

spi: i.MX: use start mode control bit ...

The i.MX SPI controller in version 2.3 can immediately start a transfer
when the txfifo is written to. In this mode we no longer have to trigger
the transfer with the xch bit which makes the code a bit simpler.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

spi: i.MX: move register defines to include/ ...

The register defines will be used by the SPI xload code, so move
them to a place where the xload code can include them.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>