defconfig: k2g_evm_defconfig: Enable Cadence QSPI controller

Enable Cadence QSPI controller support to use QSPI on K2G SoC. Also
enable Spansion flash support to access s25fl512s flash present on K2G
QSPI bus.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>