sf: params: Added support for Spansion S25FL512S_512K

Added support for Spansion chip "S25FL512S_512K".

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
spi: soft_spi: Support NULL din/dout buffers

This mirrors the conventions used in other SPI drivers (kirkwood,
davinci, atmel, et al) where the din/dout buffer can be NULL when the
received/transmitted data isn't important.  This reduces the need for
allocating additional buffers when write-only/read-only functionality is
needed.

In the din == NULL case, the received data is simply not stored.  In the
dout == NULL case, zeroes are transmitted.

Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
sf: probe: Fix quad bit set path

Currently, flash quad bit is set in "spi_flash_validate_params" and later
at the end in the same api, we write 0 to status register for few flashes,
thereby overriding the quad bit set. This fix moves the quad bit setting
outside this api in "spi_flash_probe_slave"

Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Merge branch 'master' of git://git.denx.de/u-boot-spi