ARM: dts: msm: configure the WLED sink correctly for msmcobalt platforms

WLED module supports 4 sinks but the display panel used in
msmcobalt CDP, MTP and QRD platforms needs only 2 sinks.
Configure it correctly to reduce the power consumption and
to ensure proper operation.

CRs-Fixed: 1031663
Change-Id: I75507a6f7ef409b5135afa1a913f2bee501b7b12
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>