flea3: Convert to generic board

Boards need to select CONFIG_SYS_GENERIC_BOARD in order to
prevent removal from the project.
Signed-off-by: NStefano Babic <sbabic@denx.de>

include/configs/flea3.h

@@ -22,6 +22,7 @@
 #define CONFIG_SYS_CACHELINE_SIZE	32
 
 #define CONFIG_DISPLAY_CPUINFO
+#define CONFIG_SYS_GENERIC_BOARD
 
 /* Only in case the value is not present in mach-types.h */
 #ifndef MACH_TYPE_FLEA3