app: aboot: select usb controller to be used at runtime

Instead of compile time selection, query the target at runtime
to select the usb controller to be used for fastboot.

Change-Id: Ib0081b0813589781b96b8993358223db196d1dbb
diff --git a/app/aboot/aboot.c b/app/aboot/aboot.c
index f5495f9..afab5b9 100755
--- a/app/aboot/aboot.c
+++ b/app/aboot/aboot.c
@@ -1557,7 +1557,7 @@
 #endif
 
 	fastboot_okay("");
-	udc_stop();
+	fastboot_stop();
 
 	boot_linux((void*) hdr->kernel_addr, (void*) hdr->tags_addr,
 		   (const char*) hdr->cmdline, board_machtype(),
@@ -1957,7 +1957,7 @@
 void cmd_continue(const char *arg, void *data, unsigned sz)
 {
 	fastboot_okay("");
-	udc_stop();
+	fastboot_stop();
 	if (target_is_emmc_boot())
 	{
 		boot_linux_from_mmc();