nand: Allow reinitialization

NAND devices are destroyed in between unit tests. Provide a function to
reinitialize the subsystem at the beginning of each test.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

include/nand.h

@@ -11,6 +11,7 @@
 #include <config.h>
 
 extern void nand_init(void);
+void nand_reinit(void);
 unsigned long nand_size(void);
 unsigned int nand_page_size(void);