sf: Divide spi_flash into multiple parts

Divided the spi_flash framework into mutiple parts for
- spi_flash.c:
        spi flash core file, interaction for spi/qspi driver to
        spi_flash framework.
- spi_flash_ops.c
        spi flash preffered operations, erase,write and read.
- spi_flash_probe.c
        spi flash probing, easy to extend probing functionality.

This change will support to extend the functionality in a
proper manner.

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