spi: atmel: add support to FIFOs and the internal chip-select

ChangeLog

v4:
- remove the chip-select patch from the series as it has already been applied
- reword the commit message of the DT bindings patch to better explain why we use a new DT property, "atmel,fifo-size" instead of relying on the VERSION register or the "compatible" string.
- reword the commit message of the actual FIFO patch to better explain what are the MULTIPLE and SINGLE data modes and how to use them properly.
- add Acked-by: Nicolas Ferre <[email protected]>

v3:
- replace "Alternative Command Mode" by "Chip Select Active After Transfer" in the DT bindings documentation. The "Alternative Command Mode" is a feature of the I2C controller.
- rename somes "size" variables to "num_data" to ease the distinction between the number of bytes and the number of data to transfer.

v2:
- read the Status Register to clear its RX FIFO Threshold Flag (RXFTHF) before writing into the IER to enable the RXFTHF interrupt.
- remove the reset of the FIFO Mode Register (FMR) at the end of transfers because setting the RX FIFO Threshold to 0 also sets the RXFTHF bit in SR.
- add a 3rd patch in the series to update the documentation of DT bindings.

v1:
This series of patches add support to features introduced by the Atmel sama5d2x SoC

Cyrille Pitchen (2):
spi: atmel: update DT bindings documentation
spi: atmel: add support to FIFOs

 .../devicetree/bindings/spi/spi_atmel.txt          |   8 +-
 drivers/spi/spi-atmel.c                            | 255 ++++++++++++++++++++-
 2 files changed, 252 insertions(+), 11 deletions(-)

1.8.2.2