add flash/nor/drivers.c

Encapsulates access to the flash_drivers array, providing a base
of operations for future dynamic driver module loading features.

src/flash/nor/core.c

@@ -25,19 +25,8 @@
 #include <target/image.h>
 
 // in flash.c, to be moved here
-extern struct flash_driver *flash_drivers[];
 extern struct flash_bank *flash_banks;
 
-struct flash_driver *flash_driver_find_by_name(const char *name)
-{
-	for (unsigned i = 0; flash_drivers[i]; i++)
-	{
-		if (strcmp(name, flash_drivers[i]->name) == 0)
-			return flash_drivers[i];
-	}
-	return NULL;
-}
-
 int flash_driver_erase(struct flash_bank *bank, int first, int last)
 {
 	int retval;