zephyr/Kconfig: Resolve build problem with multiple FatFs libs.

Zephyr and MicroPython both have a variant of FatFs, but having both
enabled leads to build fails.

Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>

Author: maass-hamburg

ports/zephyr/Kconfig

@@ -34,6 +34,7 @@ config MICROPY_HEAP_SIZE
 
 config MICROPY_VFS_FAT
 	bool "FatFS file system"
+	depends on !FAT_FILESYSTEM_ELM
 
 config MICROPY_VFS_LFS1
 	bool "LittleFs version 1 file system"