sf: Add FSR support to spi_flash_cmd_wait_ready

This patch adds flag status register reading support to
spi_flash_cmd_wait_ready.

Cc: Simon Glass <sjg@chromium.org>
Cc: Marek Vasut <marex@denx.de>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Hou Zhiqiang <B48286@freescale.com>
Tested-by: Jagan Teki <jteki@openedev.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>