tests: Kconfig: Added a new Kconfig for qemu_x86

The qemu doesn't have any flash drivers present in the
drivers/flash folder.
When building the tests/subsys/fs/nffs_fs_api the qemu picks
up a local file to emulate the drivers. This setup was causing the
failures in mapping required dependencies. This patch creates a
new kconfig which can be used to test out the flash drivers.

Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>