ehci-mx5/6: Make board_ehci_hcd_init() optional

A custom board_ehci_hcd_init() may be unneeded, so add a weak default
implementation doing nothing.

By the way, use simple __weak from linux/compiler.h for
board_ehci_hcd_postinit() instead of weak alias with full attribute.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/drivers/usb/host/ehci-mx6.c b/drivers/usb/host/ehci-mx6.c
index 9ce25da..1b20e41 100644
--- a/drivers/usb/host/ehci-mx6.c
+++ b/drivers/usb/host/ehci-mx6.c
@@ -159,6 +159,11 @@
 	__raw_writel(val, usbother_base + USB_H1_CTRL_OFFSET);
 }
 
+int __weak board_ehci_hcd_init(int port)
+{
+	return 0;
+}
+
 int ehci_hcd_init(int index, struct ehci_hccr **hccr, struct ehci_hcor **hcor)
 {
 	struct usb_ehci *ehci;