ahci: mediatek: add ahci driver

add AHCI driver ported from linux

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/ata/ahci_mtk.c

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
diff --git a/drivers/ata/Kconfig b/drivers/ata/Kconfig
index d8c9756..f2f8275 100644
--- a/drivers/ata/Kconfig
+++ b/drivers/ata/Kconfig
@@ -130,4 +130,12 @@
 	  onboard AHCI SATA.
 
 	  If unsure, say N.
+
+config MTK_AHCI
+	bool "Enable Mediatek AHCI driver support"
+	depends on AHCI
+	help
+	  Enable this driver to support Sata devices through
+	  Mediatek AHCI controller (e.g. MT7622).
+
 endmenu