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/drivers/block/fsl_sata.c b/drivers/block/fsl_sata.c
index ebd6261..71d7cec 100644
--- a/drivers/block/fsl_sata.c
+++ b/drivers/block/fsl_sata.c
@@ -255,6 +255,11 @@
 	return 0;
 }
 
+int reset_sata(int dev)
+{
+	return 0;
+}
+
 static void fsl_sata_dump_regs(fsl_sata_reg_t __iomem *reg)
 {
 	printf("\n\rSATA:           %08x\n\r", (u32)reg);