This commit adds the following spi transfer functions:
- spi_write
- spi_read
- spi_write_then_read
- spi_w8r8
The code has been ported from the linux kernel.
Signed-off-by: Hubert Feurstein <h.feurstein@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>