sandbox: Convert SPI flash emulation to use sf_params

At present sandbox has its own table of supported SPI flash chips. Now that
the SPI flash system is fully consolidated and has its own list, sandbox
should use that.

This enables us to expand the number of chips that sandbox supports.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>