drivers: wifi: winc1500: Add new config flag

There is a hardcoded macro in Winc1500 HAL SPI driver
that would prevent the driver from working.
This macro is now defined only based on KConfig entry.
This KConfig entry is by default not set.
To enable, set "CONFIG_WINC1500_DRV_USE_OLD_SW=y"
in proj.conf or board.conf

Signed-off-by: Raja D. Singh <rdsingh@iotwizards.com>