arm: defconfig: Set USB current limit to 500 for msm8909

Set required flag CONFIG_USB_GADGET_VBUS_DRAW to 500 so that
composite layer can update drawing current to underlying USB
driver correctly after USB is configured.

Change-Id: I11a186d34b53a8b5790c7aeaa23b0329b4ba8266
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>