OMAP3 SPI : Fixed bugs related to SPI transfer

Added posted writes (read after writes) to effect the
change immediately for channel confiuration and channel
enable register

Disable the channel to purge receieve data in TX_ONLY
mode transfer otherwise rx data will get affected by
the next immediate RX_ONLY mode transfer

Wait for the EOT bit to be set after last byte has been
loaded to TX shift register in the the TX_ONLY mode.This
ensures TX data has been completely shifted out

Disable the channel in RX_ONLY mode before reading the
last data from  RXX register to prevent the SPI slave
to transmit next word

Signed-off-by: Ajoy Kumar Das <akdas75@yahoo.in>
Cc: Tom Rini <trini@ti.com>
Cc: jacopo mondi <j.mondi@voltaelectronics.com>