am335x, dfu: add DFU_MANIFEST_POLL_TIMEOUT to the siemens boards

as the siemens boards use dfu for updating a nand ubi partition
add DFU_MANIFEST_POLL_TIMEOUT to them, so dfu host waits after
complete transfer of the new image for DFU_MANIFEST_POLL_TIMEOUT
ms before sending again an usb request. So the board have enough
time to erase rest of the nand sectors.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>

include/configs/siemens-am33x-common.h

@@ -265,6 +265,7 @@
 #define CONFIG_DFU_NAND
 #define CONFIG_CMD_DFU
 #define CONFIG_SYS_DFU_DATA_BUF_SIZE	(1 << 20)
+#define DFU_MANIFEST_POLL_TIMEOUT	25000
 
 #endif /* CONFIG_SPL_BUILD */