feat(stm32mp2): add STM32MP_USB_PROGRAMMER compilation

Add minimal compilation step when enabling STM32MP_USB_PROGRAMMER flag
on STM32MP2. Add DWL_BUFFER_BASE in platform.mk and the compilation
of the new file plat/st/stm32mp2/stm32mp2_usb_dfu.c (just stubs for
the moment).

Signed-off-by: Pankaj Dev <pankaj.dev@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I8891ff23ddc3d40d7477ada3e49e439dd8af8316
diff --git a/plat/st/stm32mp2/stm32mp2_usb_dfu.c b/plat/st/stm32mp2/stm32mp2_usb_dfu.c
new file mode 100644
index 0000000..e967964
--- /dev/null
+++ b/plat/st/stm32mp2/stm32mp2_usb_dfu.c
@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2024, STMicroelectronics - All Rights Reserved
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stddef.h>
+
+#include <drivers/usb_device.h>
+
+#include <usb_dfu.h>
+
+struct usb_handle *usb_dfu_plat_init(void)
+{
+	return NULL;
+}
+
+uint8_t usb_dfu_get_phase(uint8_t alt)
+{
+	return 0;
+}