Revert r21912 : "Storage API : remove undeeded target-specific functions"

After a discussion mixed on mailing list and irc, it was agreed that
more abstraction for plugins is better (so developers don't have to add
a check to HAVE_DISK_STORAGE when writing disk-specific code)

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21923 a1c6a512-1295-4272-9138-f99709370657

firmware/target/arm/ata-nand-telechips.c

@@ -900,3 +900,16 @@ long nand_last_disk_activity(void)
 {
     return last_disk_activity;
 }
+
+void nand_sleep(void)
+{
+}
+
+void nand_spin(void)
+{
+}
+
+void nand_spindown(int seconds)
+{
+    (void)seconds;
+}

firmware/target/arm/s5l8700/ata-nand-s5l8700.c

@@ -64,6 +64,29 @@ int nand_write_sectors(IF_MV2(int drive,) unsigned long start, int count,
     return 0;
 }
 
+void nand_spindown(int seconds)
+{
+    (void)seconds;
+}
+
+bool nand_disk_is_active(void)
+{
+    return 0;
+}
+
+void nand_sleep(void)
+{
+}
+
+void nand_spin(void)
+{
+}
+
+int nand_soft_reset(void)
+{
+    return 0;
+}
+
 void nand_enable(bool on)
 {
     (void)on;