[ARM] 4939/1: [CSB637] Update defconfig to use gpio-led

Updates the CSB637 platform's D1/PB2 LED to use gpio-led by default.
Signed-off-by: NBill Gatliff <bgat@billgatliff.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>