uboot-imx

sf: Rename spi_flash files

Renamed:
spi_flash.c -> sf.c
spi_flash_internal.h -> sf_internal.h
spi_flash_ops.c -> sf_ops.c
spi_flash_probe.c -> sf_probe.c

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>