sata: implement reset_sata for dwc_ahsata

Add reset_sata() to the sata driver interface and implement it
for dwc_ahsata. This function cleans up after sata_init(), and
therefore accepts a device number like sata_init() does.
A dummy implementation is provided for the rest of the drivers.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/include/sata.h b/include/sata.h
index 38f4b4a..c2bbe1a 100644
--- a/include/sata.h
+++ b/include/sata.h
@@ -3,6 +3,7 @@
 #include <part.h>
 
 int init_sata(int dev);
+int reset_sata(int dev);
 int scan_sata(int dev);
 ulong sata_read(int dev, ulong blknr, lbaint_t blkcnt, void *buffer);
 ulong sata_write(int dev, ulong blknr, lbaint_t blkcnt, const void *buffer);