ARM: dts: msm: Update WLED configuration for sdm660

Update wled string configuration to use string1 and string2
corresponding to the LED strings connected to the panels
used with SDM660 MTP, QRD, CDP devices.

Change-Id: Id26aa1a40c6669313641bc79410d28118d9fbfd6
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>