defconfig: sdm855: Enable QCOM_SPMI_WLED support

Enable WLED driver support on sdm855 platforms needed for the
backlight control for display panels.

Change-Id: I6fa0e745587a3e82864fb7e42f5ada41b42faa13
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>