ARM: dts: msm: add GPIO support for flash LED for MSMGOLD

On MSMGOLD, GPIO 33 is used to control rear flash LED, and
GPIO 50 is used to control front flash LED.
This change adds the support for rear flash LED only.

Change-Id: Ie245bf9495feb220ae815a9e803ccc61a6a7b29a
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>