api/spi: Add EEPROM configuration bit

EEPROM read mode is a specific mode where the controller will TX a
command to the slave, and once done, will read as many bytes requested.
The gain relies in the controller generating all necessary dummy bytes
by itself to read data the from slave, it will only generate RX
interrupts. Thus reducing CPU work.
Obviously TX and RX buffers should be relevantly provided by the user.

If not supported by the controller, the driver can still work (it will
have to generate the dummy bytes) and thus -EINVAL should not be
returned for that configuration bit.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>