uboot-phytec

mtd: spi: Drop sf.c

spi_write_then_read, will manage to do the respective
spi_xfer based on the tx_buf, rx_buf so drop the
legacy spi_flash_read/write/cm code.

Tested-by: Adam Ford <aford173@gmail.com> #da850-evm
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>